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NRLF 




PUKL.ISHER & IMPORTER 



UNIVERSITY Of 
CALIFORNU 




THE LIBRARY 

OF 

THE UNIVERSITY 
OF CALIFORNIA 



BEQUEST OF 

Alice R. Hilgard 



V 










LITHOLOGY. 



LOIfDOK 

FEINTED BY SPOTTISWOODB AITI) CO. 
NBW-STEEBT 8QITABE 



ROCKS 

CLASSIFIED AND DESCRIBED. 

Iwatitt on i 



BY BEENHAED VON COTTA. 



AN 'ENGLISH EDITION 

BY 

PHILIP HENRY LAWRENCE. 



WITH ENGLISH, GERMAN, AND FRENCH SYNONYMS. 



REVISED BY THE AUTHOR. 



LONDON : 

LONGMANS, GREEN, AND CO. 
1866. 



LITHOLOGY, or a Classified Synopsis of the 
Names of Kocks ar-d Minerals, also by Mr. LAWKENCE, 
adapted to the present work, may be had, price 5s. or 
printed on one side only (interpaged blank) for use in 
Cabinets, price 7s. 



7 



GIFT 



TRANSLATOR'S PREFACE. 



IN presenting this work to English readers, I wish to 
acknowledge the kind assistance I have received from 
Professor Jukes and Mr. Bristow in my own country, from 
M. Daubree and M. Guyerdet in France, and last, but 
not least, from the distinguished author, Professor Cotta 
himself, and from Mr. Stelzner, of Freiberg, to whose 
valuable assistance I owe most of what is good in the 
new arrangement of the Mineralogical part of the work. 
For the many imperfections which, in spite of much care, 
will probably be found, I am alone responsible. Never- 
theless, I hope that this work may in some measure 
supply a want which has been long felt in our geological 
literature. 

I trust that allowance will be made for the difficulties 
of a translator if, in some instances, terms have been used 
in this work in a slightly extended or even different 
sense from that of some English authors. This has never 
been done without much consideration, and what appeared 
to me absolute necessity in rendering the meaning of my 
author, and in the absence of an exact equivalent for the 
German term in our accepted geological language. 

M860773 



vi TKANSLATOK'S PKEFACE. 



The juxtaposition of the English, German, and French 
equivalent names for each rock, although frequently pre- 
senting doubts and difficulties, will, I trust, in the main 
meet with acceptance, in which case it cannot fail to prove 
useful. 

Scientific names are the coin in which enquirers must 
exchange their ideas ; and if they can be made to corre- 
spond in different countries, the gain to science will be 
great. Such correspondence is as important in its way 
as the assimilation of currency for the operations of 
commerce. Should this object have been in any way 
promoted by the present work, my most sanguine expec- 
tations will have been fulfilled. 

I may here mention that, in furtherance of the same 
object, I have published, separately, a catalogue of the 
names of Rocks in the three languages. This catalogue, 
which is an outline of this work, may, perhaps, prove 
useful to collectors. 

P. H. LAWRENCE. 

LONDON : January 1866. 



AUTHOR'S PREFACE 

TO THIS EDITION. 



BEFORE my friend the Translator undertook the transla- 
tion of this work, I had collected materials and made 
certain alterations with a view to a third edition. 

The Translator himself, in the course of his labour, 
proposed jcertain alterations, which were adopted with 
my entire concurrence. 

As far as my knowledge of the language enables me to 
judge, after a careful perusal, the translation appears to 
me to be very accurate. . 

This English edition may therefore be considered as 
the third edition of my original work, although, if the 
appearance of a third German edition should be delayed 
for some time longer, there will doubtless be new matter 
and fresh alterations to be introduced; for Science 
marches with uninterrupted steps towards new fields 
of discovery, mid every year alters its aspect. 

In a system of Lithology, however, most of the names 



viii AUTHOR'S PREFACE. 



which are in use will probably remain, and one chief 
object of this book is to define these so as to render 
intelligible the ideas which each name should convey ; 
and both Author and Translator are actuated by the 
desire and ambition of arriving, as far as may be possible, 
at a common ground for all nations in respect of the 
important matter of rock-nomenclature. 

B. COTTA. 

FBEIBEKG : January 1866. 



CONTENTS. 



PART I. 
CHAPTER I. 

PAGE 

MINERALS ...... 1 

I. Oxygen Compounds . . . . .5 

A. Oxides of Silicon and Aluminum (Earths) . . 6 

B. Silicates ..... 

a. Felspar Section ..... 8 

Orthoclastic Felspars . . . , 9 

Plagioclastic Felspars . . . .10 

Leucite and Nepheline Group . . .14 

b. Augite Section . . . . . K> 

c. Mica Section . . . .22 

d. Hydrous Magnesian Silicates (Talc Section) . 24 

e. Zeolite Section (Non-Magnesian Hydrous Silicates) 28 

The Monometric Zeolites 

Hexagonal Zeolites . . . .30 

Trimetric Zeolites . . . .31 

Monoclinic Zeolites . . .32 

f. Andalusite Section . . .34 

g. Garnet Section ... .38 

C. Tantalates (or Columbates), Titanates, Vanadates . 46 

D. Sulphates .... 

a. Anhydrous Sulphates . .47 

b. Hydrous Sulphates . .49 

E. Borates . . . -62 



CONTENTS. 



I. Oxygen Compounds continued. PAGE 

F. Phosphates . . ... .53 

a. Anhydous Phosphates . -. . .53 

b. Hydrous Phosphates . . .54 

G. Nitrates ... ... . . 55 

H. Carbonates . . . . . .56 

a. Anhydrous Carbonates . . . .56 

b. Hydrous Carbonates . . . .59 
I. Oxides of the Elements of the Hydrogen Group . 60 

a. Anhydrous Oxides . . . . .60 

b. Hydrous Oxides . . . . .66 
II. Fluorides and Chlorides . . . . .67 

III. Sulphurets. Arseniurets . . . . .69 

IV. Native Elements . . . . . .74 

V. Kesins. Organic Compounds . . . .76 

CHAPTER H. 

ANALYSIS OP ROCKS . . . . . .78 

Microscopic Analysis . . . . . .78 

Magnetic Analysis . . . . . .78 

Chemical Analysis . . . . . .79 

CHAPTER III. 

PHYSICAL STRUCTURE OP ROCKS . . . .87 

Texture ....... 87 

Particular States of Rocks . . . . .95 

Concretionary Structure . . . . .98 

Special Forms of External Structure . . . .99 

Jointed Structure . . . . . . 103 

STRATIFICATION OP ROCKS . . . . 105 

SHAPE AND BEDDING OP ROCK MASSES . . . . 106 

CHAPTER IV. 

GEOLOGICAL FORMATIONS AND GROUPS OF Roczs . . Ill 

CHAPTER V. 

TRANSITIONS AND TRANSMUTATIONS 120 



CONTENTS. X 

PART II. THE ROCKS. 
INTRODUCTORY CHAPTER. 

PAGE 

CLASSIFICATION . . /'" . . . .123 

CHAPTER I. 

IGNEOUS ROCKS . . ', * 127 

Basic Igneous Rocks ...... 131 

(1) Volcanic . . . ." '. . 131 

Basaltic Rocks ..... 132 

(2) Plutonic . . . . . . .144 

Greenstones ...... 146 

Porphyrite Group ..... 168 

Mica Trap Rocks . . . . .173 

Syenite Group ; . ,. ^ .176 

Acidic Igneous Rocks . . . . 182 

(1) Volcanic . . . . . .182 

Trachyte Group . . . , .183 

Phonolite Group ' .. >, . . . 198 

(2) Plutonic . . . . .201 

Granitic Group . .... 201 

CHAPTER H. 

METAMORPHIC CRYSTALLINE SCHISTS .... 227 

Felspar Group . . . . . 229 

Quartz Group . ..... 241 

Chlorite, Talc, and Hornblende Group . . 249 

Schists indistinctly Crystalline . . . 264 

CHAPTER HI. 

SEDIMENTARY AND FRAGMENTAL ROCKS . . 259 

Argillaceous Group . . . 263 

Marl Group . . . 

Limestone Group . 274 

Gypsum and Anhydrite . 290 

Fragrnental Rocks . .294 

Conglomerates . 302 



Xii CONTENTS. 

CHAPTER IV. 

PAGE 

ROCKS OF SPECIAL CHARACTER OK BEDDING . . . 313 

Serpentine Group -,' '.^ . . 314 

Garnet Group . .318 

Greisen and Schorl Group . . . . 320 

Carbonaceous Group . . . r \ . 324 

Ironstone Group . . . . . 340 

CHAPTER V. 

MINERALS AS ROCKS . 347 



PAKT III. 

OBSERVATIONS ON THE PROCESSES OF ROCK FORMATION IN 

NATURE . . . . .- A-. . 359 

Igneous Rocks ... u? v . 361 

Sedimentary Rocks . . . "> .' :. - . 374 

Metamorphic Crystalline Schists . . ; > . . 378 

Mineral Veins and Veins of Ore 392 



CONCLUSION , 393 



LITHOLOGY. 

PART L 
CHAPTER I. 

MINERALS. 

THE SEVERAL SUBSTANCES which form the materials 
of the earth's crust are termed 'Rocks,' the idea of a 
solid rocky substance not being necessarily implied. Most 
of what we call rocks are no doubt of a firm and solid 
character, but some consist only of soft or loose aggregates 
or accumulations of their component parts. 

These component parts are always minerals ; that is to 
say, all rocks are mineral aggregates, consisting of minute 
mineral parts more or less solict and more or less intimately 
and firmly united, knit, or cemented together. By this 
definition it will be seen that we exclude the animal and 
vegetable kingdoms ; it may therefore be well to add 
that under the term mineral we include all mineralised 
remains of organic bodies. 

Most rocks are made up of parts of two or more different 
minerals, in which case they are termed composite. Some 
rocks, however, consist essentially of particles of one mine- 
ral only, such for instance as limestone ; these, in contra- 
distinction to the composite, are termed simple rocks. 

The composite as well as the simple rocks not unfre- 
quently contain subordinate ingredients, besides those 
which are essential to their character. These subordinate 
ingredients are termed accessory or non-essential. In 
most cases they are inconsiderable in quantity, or they 
only occur locally and do not appreciably alter the nature 

B 



2 MINEKALS. 

of the rock ; but sometimes these accessory ingredients 
impart a special character to it, and so to a certain extent 
pass into essentials. Their presence creates the varieties 
of species. 

The constituent minerals (whether accessory or essen- 
tial) of any given rock either occur in separate crystals or 
particles distinguishable by the naked eye, or they consist 
of small finely divided particles so intimately blended to- 
gether as apparently to form a homogeneous mass ; never- 
theless, in the latter case, their separate existence may be 
generally recognised by magnifying power. 

The first and principal requisite for the student of 
Lithology is to be able to recognise and determine the 
minerals of which a given rock consists. This is in many 
cases no easy task ; he must therefore have a competent 
knowledge of mineralogy. Not with a view adequately to 
supply the want of such knowledge, but by way of intro- 
duction to our subject, rnd for the purpose of reference 
in the absence of more comprehensive works, we propose 
to give in this chapter a brief notice of the principal 
minerals with which we have to do in examining the 
structure of rocks, adding such particulars as are more 
especially useful for our present purpose. 

The number of these principal minerals is relatively 
very small. They may be classed under the following 
comprehensive names : FELSPAR, QUARTZ, MICA, 
HORNBLENDE (Amphibole), PYROXENE (Augite), 
CALCSPAR, and DOLOMITE. The following occur less 
frequently : CHLORITE, TALC, LEUCITE, NEPHELINE, 
OLIVINE, TOURMALINE, GARNET, GYPSUM, COAL, some 
SULPHURETS, and some IRON ORES. 

The number of the accessory ingredients is very much 
greater, and indeed almost unlimited; that is to say, 
under certain circumstances almost every known mineral 
may occur as an accessory in any rock, and the essential 
ingredients of one rock frequently occur as accessories in 
another rock. But although we may say with truth that 
the number of the accessory minerals is without limit, yet 
in fact only about a quarter of the number of hitherto 
known minerals occur in rocks so abundantly and fre- 
quently as to be specially noticed in a treatise of Lithology. 

One consideration is particularly deserving the atten- 



MINERALS. 3 

tion of the scientific observer of rocks ; we refer to what 
is termed by Breithaupt the ' Paragenesis ' of minerals. 
By this is meant the law of mutual association or repulsion 
of certain minerals. It is well known to mineralogists 
that the presence of one mineral very frequently denotes 
the neighbourhood of another, and, vice versa, that the 
presence of some minerals forbids the simultaneous pre- 
sence of certain others. 

In 1849 Breithaupt first treated this subject, and pub- 
lished in his ' Paragenesis der Mineralien ' a great number 
of remarkable instances of this law. We may, for the sake 
of illustration only, select the following as examples : 

1. Minerals which are usually associated together: 
Quartz and mica ; orthoclase, quartz, and mica ; ortho- 
clase and oligoclase ; labradorite and augite ; orthoclase 
or oligoclase and hornblende ; hornblende and epidote. 

2. On the other hand, quartz and augite appear each to 
exclude the presence of each other ; also (according to 
Both) labradorite and hornblende (?). 

We are unable to pursue this important subject in this 
place ; we have been compelled to confine ourselves, in 
the following notice, to appending a few of the more im- 
portant instances of paragenesis to the description of 
some of the principal mineral classes. 

As to the much-debated question of classification of the 
minerals, we have adopted one which appeared to us best 
suited for our present purpose ; it is not exactly that of 
any one author. We have -placed a few of those minerals 
first which are of the most frequent occurrence ; otherwise, 
the arrangement adopted will be found to correspond in 
several respects with Dana's ' System of Mineralogy.' 

The following are the abbreviations we have used : 
H. for hardness; S.G. for specific gravity ; Cp. for 
chemical composition ; Bp. for before the blowpipe. The 
quantities of the chemical elements we have given in 
round numbers, as being sufficient for our present pur- 
pose. In the chemical formula? we have, for the sake of 
convenience, adopted the abbreviations usual on the Con- 
tinent, of expressing the oxygen atoms by dote, and a 
stroke to denote a double atom ; thus, Fe' 2 O 3 is written 
Fe. W"e subjoin the following list of formulae for the 
elementary bodies and their simple compounds: 

B 2 



MINERALS. 



CHEMICAL SYMBOLS. 



Al Aluminum, Aluminium 

Al Alumina 
Ag Silver 
As Arsenic 

As Arsenic Acid 
Au Gold 
Ba Barium 

Ba Baryta 
B Boron 

B Boracic Acid 
Ca Calcium 

Ca Lime 
C Carbon 

C Carbonic Acid 
Cb Columbium, Niobium 

Cb Columbic Acid 
Ce Cerium 

Ce Protoxide of Cerium 
Cl Chlorine 

HC1 Hydrochloric Acid 
Cr Chromium 

Cr Oxide of Chromium 

Cr Chromic Acid 
Co Cobalt 

Co Oxide of Cobalt 
Cu Copper 

Cu Oxide of Copper 
Fe Iron 

Fe Protoxide of Iron 

Fe Peroxide of Iron 
F Fluorine 

HF Hydrofluoric Acid 
G Beryllium or Glucinum 

G Glucina 
Hg Mercury 
H Hydrogen 

H Water 
K Potassium 

K Potassa 
La Lanthanum 

La Protoxide of Lanthanum 



Li Lithium 

Li Lithia 
Mg Magnesium 

Mg Magnesia 
Mn Manganese 

Mn Protoxide of Manganese 

Mn SesquioxideofMangane.se 
Na Sodium 

Na Soda 
Ni Nickel 

Ni Protoxide of Nickel 
N Nitrogen 

N Nitric Acid 
Oxygen 
P Phosphorus 

P Phosphoric Acid 
Pb Lead 

Pb Oxide of Lead 
Se Selenium 
Si Silicon 

Si Silica 
Sn Tin 

Sn Oxide of Tin 
Sr Strontium 

Sr Strontia 
S Sulphur 

S Sulphuric Acid 
Ta Tantalum 

Ta Tantalic Acid 
Ti Titanium 

Ti Oxide of Titanium 

ti Titanic Acid 

V Vanadium 

Y Yttrium 

Y Yttria 

Zn Zinc 

Zn Oxide of Zinc 

Zr Zirconium 

Zr Zirconia 



QUARTZ. 5 

I. Oxygen Compounds. 

A. OXIDES OF SILICON AND ALUMINUM (EARTHS). 

1. Quartz. Rhombohedral crystals, usually combinations 
of two rhombohedrons and hexagonal prism. Cleavage accord- 
ing to the planes pf one rhombohedron, but imperfect. Frac- 
ture conchoidal to uneven and splintery. H.=7. S.G.=2'5 
2 '8. Colourless and limpid, or variously coloured, forming many 
varieties. Lustre vitreous, sometimes resinous, especially on 
the surfaces of fracture. Cp. = Si, with admixture of minute 
particles of colouring oxides. Two modifications of chemical 
composition are distinguished by their different degrees of solu- 
bility. The one is insoluble in water and in every acid, except 
hydrofluoric acid ; the other is soluble in water at high tem- 
peratures, especially in the presence of other acids and alkalies. 
The insoluble variety of quartz may, in process of time, be- 
come converted into the soluble by the contact-influence of 
infiltrated moisture. The soluble variety of quartz, in small 
proportions, is found in many waters of springs and rivers, 
and in the sea, e. g., at the Geysers in Iceland, up to T8 | 00 
per cent, and in sea- water to -nrurjuir P er cent - Bp. infusible ; 
with soda fusible to a clear glass with effervescence. Not 
affected by phosphoric acid. 

(a) Common Quartz, the most abundant of all minerals. 

It is found : 

(a) As an independent rock. (See post.) 
(ft) As essential ingredient of many crystalline rocks, espe- 
cially the plutonic. In most kinds of granite, in greisen, 
and in the crystalline schists it is found in crystalline 
grains. In quartz-porphyry, rhyolite, and, excep- 
tionally, in some kinds of granite (e.g. St. Austell, 
Cornwall), it is perfectly crystallised. 



r MINERALS. 

(y) As accessory constituent mass of some rocks (snch as 
crystalline schists), in form of veins and swellings, or 
clothing the interior of geodes in other rocks (e.g. in 
the granites of Switzerland, Carrara marble, the 
variegated sandstone of the Schwarzwald, &c.) The 
quartz of the geodes is frequently in the form of 
transparent crystals (rock crystal), or in greyish- 
brown to black crystals (smoky quartz, false topaz). 

(S) As principal ingredient of many fragmental rocks 
(sandstones, conglomerates). As sand and gravel in 
beds of deposit. 
(It) Amethyst. Violet, coloured by the oxide of manganese. 

(c) Chalcedony. An intimate admixture of crystalline and 

amorphous silica. 

(d) Agate. A variegated combination of common quartz, 

amethyst, jasper, carnelian, and other varieties of quartz, 
arranged in alternate stripes or layers, or irregularly 
mixed together. 

\b, c, and d chiefly occur in the geodes of volcanic rocks (in 
Iceland, Faroe Islands, the Brazils, &c.), or in metallic veins 
(e.g. in Saxony).] . 

(e) Jasper. Very frequently in globular masses (ball-jasper) 

coloured red by the peroxide of iron ; found in the bog 
iron-ore of Briesgau, in Germany, and elsewhere, or 
coloured yellowish-brown by the hydrated oxide of 
iron. (Occurs in form of pebbles, e.g. in the sand 
of the Nile and Desert.) Jasper sometimes forms 
subordinate layers in other rocks. 

(/) Flint. Coloured greyish-blue, or black, by presence of 
carbon. Occurs as a concretionary formation in sedi- 
mentary limestone rocks, e.g. in the Chalk of England 
and France, in the Upper White Jurassic of the Fran- 
conian Switzerland in Bavaria. 



OPAL. 7 

(g) Chert, Homstone is distinguished from flint by its more 
splintery fracture, by its transparency, and colour, 
which is grey, yellow, green, red, or brown, resembling 
jasper. It frequently furnishes the material of fossils, 
especially of fossil wood (woodstone). 

There are at least three different processes in nature which 
have contributed to the formation of quartz. 

Quartz has been formed: 1. By organic agency. The 
siliceous needles (spiculae) of sea-sponges, the siliceous 
shields of certain Protozoa (kieselguhr, tripoli), and many 
plants (especially grasses) either contain quartz, or consist 
entirely of quartz. 2. By agency of water. The concre- 
tionary formations of flint, jasper, &c., the crystals and 
amorphous quartz contained in geodes, and many formations 
at springs which consist of pure quartz, and are termed 
freshwater quartz. 3. By hydroplutonic agency. Daubree 
has actually produced quartz, by way of experiment, through 
the agency of steam on chloride and fluoride of silicon. 
Many kinds of quartz have no doubt been produced by pure 
plutonic agency. 

2. Opal. Amorphous, massive. Fracture conchoidal to un- 
even; friable. H.=5-5 6-5. S.G.=1'9 2-3. Colourless or 
variegated with rich play of colours. Transparent to opaque. 
Lustre vitreous, also resinous. Possesses many varieties, dis- 
tinguished by their different colours and degrees of trans- 
parency. Cp. amorphous Si combined with water, in varying 
proportion (up to 13 per cent.), and small quantities of colour- 
ing matter. It is distinguishable from quartz by being almost 
entirely soluble in potash ley, in matrass yields water. Bp. most 
kinds of opal decrepitate ; otherwise behaviour like quartz. 

Occurrence and Mode of Formation. Opal is never an essen- 
tial ingredient of rocks, but is of very frequent occurrence 



8 MINERALS. 

as a secondary product, furnishing the interior of small 
nests, and filling vesicular cavities in volcanic rocks, or cloth- 
ing the surfaces of clefts in the same rocks. In these 
and similar cases the opal is a product of exfiltration from 
the rock in or near which it occurs. Thus, the precious opal 
found in the trachytic rocks of Hungary, the colourless 
hyalite in clefts of basalt and lava (Bohemia, Auvergne). 
In rare cases, however, opal forms independent layers of 
small extent (riband opal) in siliceous rocks, e. g. in the 
tripoli of Bilin. The variety known as menilite occurs in 
knobs and layers embedded in the adhesive slate of Menil 
Montant, Paris. 

3. Corundum. Occurs in rhombohedral crystals, or gran- 
ular aggregates (emery). Cleavage basal, also rhombohe- 
dral in various degrees of perfection. Fracture conchoidal 
to uneven and splintery. H. 9. S.G.=3'9 4*2. Colour- 
less or coloured blue (sapphire), red (ruby), or cloudy 
(corundum). Lustre vitreous, and frequently, on the basal 
cleavage surface, mother-of-pearl lustre. Transparent to 
translucent. Cp.=Al, with small quantities of Mg, Ca, Si. 
Bp. infusible when alone, perfectly fusible with borax, but not 
without difficulty ; not affected by acids. Occurs as an 
original product accessorily in many rocks (granite of Silesia, 
basaltic lava of Medermendig on the Rhine, dolomite of 
the St. Grotthard). The precious varieties are chiefly found 
in alluvial beds (Ceylon, China). Emery forms separate 
masses of deposit in the talcose schist (Naxos, Saxony) . 

B. SILICATES. 

(a) FELSPAR SECTION. 

The felspars are, after quartz, the most important of all 
ingredients of rocks. We distinguish two principal kinds 
of felspar, the orthoclastic (monoclinic), the two most per- 



FELSPAR. 9 

feet cleavage planes forming an angle of 90, and the pla- 
gioclastic (triclinic) with an angle of less than 90. All 
felspars have a great tendency to form twin crystals, and 
this duplication occurs in them in a very marked manner, 
and according to six different laws. 

Orthoclastic Felspars. 

4. OrtJioclase. Monoclinic. Cleavage basal and clinodia- 
gonal, very perfect in both directions, hemiprismatic, im- 
perfect. Fracture conchoidal to uneven and splintery. 
H.=6. S.G. = 2*4 2*62. Colourless, sometimes limpid, more 
frequently coloured, especially reddish, yellowish, rarely 
green (amazon stone coloured by copper). Lustre vitreous, 
frequently with mother-of-pearl lustre on the most perfect 
cleavage surfaces. Possesses every degree of transparency, 
sometimes with iridescence or play of colours. Cp.=KSi + 
AlS'i 3 with 65Si, 18AJ, and 17K. A portion of the Al is 
frequently replaced by Fe, or Mn, and a portion of the K is 
sometimes replaced by Na or Ca. Bp. fusible with difficulty, 
and only at the edges, where it forms a dull porous glass. 
The varieties which contain soda colour the flame yellow. 
In microcosmic salt it is only soluble with difficulty, leaving 
behind a skeleton of silica. With cobalt solution the fused 
''dges are coloured blue. Not susceptible to the action of 
acids. 

Varieties of Colour and Lustre. 

(a) Adularia. Colourless, or only slightly coloured, with 
bright lustre, transparent to semi-transparent. Essen- 
tial ingredient of the adularia-granite and adularia- 
gneiss abundant in the Alps, also frequently found in 
the geodic cavities of granitic rocks (St. Gotthard). 

(6) Common Felspar (Pegmatolite, Microdine). Variously 
coloured, less lustrous than adularia, translucent to 



10 MINERALS. 

opaque. A characteristic ingredient of very many 
rocks, especially amongst the phitonie, such as granite, 
.gneiss, syenite, porphyry. Frequently large felspar 
crystals (such as the so-called Carlsbad twins) occur 
porphyritically embedded in an otherwise regularly 
constituted rock (e.g. in the granite of Carlsbad in 
Bohemia, and of Cornwall, porphyry of Ilmenau), or 
larger crystals clothe the sides of geodes (as in the 
granite of Baveno and the rocks of the Mourne Moun- 
tains, in Ireland). 

(c) Sanidine. Colour greyish- and yellowish-white, also 
grey. Lustre vitreous, very bright, transparent, trans- 
lucent. The crystals are very often split and creviced. 
It forms a very characteristic ingredient of genuine 
volcanic rocks, and only occurs in these. Thus it is 
found in phonolites, trachytes, pitchstones, obsidian, 
and lavas. Sometimes it occurs porphyritically in 
large tabular crystals, as in the trachyte of Dra- 
chenfels. 

Plagioclastic Felspars. 

All plagioclastic felspars are triclinic ; they cleave perfectly 
according to the base and the brachydiagonal, imperfectly 
according to the hemiprism. 

5. Albite. Fracture uneven. H.=6 6'5. S.G. - 2'59 
2 ! 65. Colourless or light red, yellow, green, or brown. Lustre 
vitreous ; mother-of-pearl lustre on the basal cleavage sur- 
faces. Transparent, translucent. A white and usually 
semi-opaque variety termed pericline, is distinguished by 
its constant crystallographic habitus. Cp.==NaSi + AlSi 3 == 
69Si + 19AH-12;N"a. The Na is frequently in part replaced 
by Ca, K, or Mg. Bp. it fuses with difficulty, colouring the 
flame yellow. It is scarcely affected by acids. Albite is 



FELSPAR. 1? 

frequently found associated in parallel growth with ortho 
clase. It is likewise a characteristic ingredient of many 
diorites and granites. Exceptionally crystals of albite are 
found in compact limestone (Col du Bonhomme). 

6. Oligoclase. Fracture uneven. H.=6. S. G. = 2'58 
2*69. Colour greyish, yellowish, or greenish. Lustre upon 
the principal cleavage surface vitreous, otherwise resinous. 
Usually is much weathered, and in that state dull ; in its 
fresh state translucent at the edges. Cp. = NaSi-i- AISi 2 = 
62S1 + 24Al + 14Na, The Na replaced in part (up to 6 per 
cent.) by Ca, K and small quantities of Fe or Mn. Bp. fuses 
much more easily than orthoclase and albite, forming a clear 
glass. Little attacked by acids. Oligoclase is an essential con- 
stituent of diabase, diorite, and kersantite ; it is frequently 
associated with orthoclastic felspars as a constituent of many 
kinds of granite (Stockholm), syenite (Dresden), porphyry 
(Southern Tyrol), and trachytes (Hungary). 

Andesine may be considered as an oligoclase rich in lime. 
It has much the outward appearance of albite. It is an 
ingredient of many trachytic rocks of the Andes, and likewise 
of many crystalline rocks of the Vosges. 

7. Labradvrite. H. = 6. .S.G. = 2'67 276. Barely co- 
lourless, usually grey, reddish, bluish or otherwise coloured ; 
usually displays a rich play of colours. Lustre vitreous, 
sometimes resinous ; translucent, but usually only at the 
edges. Cp. = RSi + AISi = 53Si + 30A1 + 12Ca + 5Na. Bp. 
fuses somewhat more readily than oligoclase to a colour- 
less glass. Unlike other felspars, its powder is thoroughly 
soluble in heated muriatic acid. Labradorite is an essential 
constituent of many, and especially of the augitic, rocks, 
e. g. dolerite, basalt, gabbro (Isle of Skye), hypersthenite, 
and many lavas of Etna. 

Saussurite (jade) is probably only an impure labradorito. 



12 MINERALS. 

bearing somewhat the same relation to it as felstone to 
orthoclase. It remains unchanged by acids, occurs only in 
compact or finely granular masses, and forms an essential 
constituent of many kinds of gabbro and greenstones. 

8. Anorthite.H.= 67. S. G. = 2'66 278. Colour- 
less, white. Lustre, mother-of-pearl on the cleavage surfaces, 
otherwise vitreous; transparent to translucent. Cp.= R/ 3 Si 
+ 3A1S1 = 43Si + 37Al + 20Ca. The Ca replaced by Mg, K, 
and Na to the extent of 5 per cent. Anorthite is completely 
soluble by concentrated muriatic acid, without gelatinising, 
but is distinguished from labradorite by its being more diffi- 
cult of fusion. It is an essential constituent of the orbicular 
diorite (Kugeldiorit) of Corsica and of many ancient lavas 
(Monte Somma). It is also found in meteoric stones. 

Some Aids for distinguishing the Felspar Species. 

(a) Crystallographic Signs. When the light is brought to 
play on the basal cleavage plane of the orthoclastic fel- 
spars it presents an unbroken surface, or in case of twin 
crystals (according to the Carlsbad law) is double ; 
whereas in the case of the plagio clastic felspars a fine 
parallel striping is usually observed, occasioned by the 
parallel growth of numberless individual crystals as thin 
as leaves of paper. This striping, when observable, is a 
very characteristic sign, but its absence is not equally so. 

(/3) Signs of Paragenesis. The following minerals are fre- 
quently found in comparing : Orthoclase with oligo- 
clase ; orthoclase and oligoclase with hornblende ; 
labradorite with pyroxene. 

On the other hand, we seldom or never find together : 
the alkali felspars (Nos. 4. 5, 6) and the calcareous 
felspars (Nos. 7, 8) ; or orthoclase with pyroxene ; 
oligoclase with leucite and nepheline ; labradorite with 



FELSPAR. 13 

hornblende ; labradorite or anorthite with quartz or 
leucite. 

(y) The weathering of felspars is noteworthy, and is parti- 
cularly useful for purposes of distinction where two 
species are found together in one rock. Labradorite 
and oligoclase weather more readily than orthoclase, 
orthoclase more readily than albite. Bearing this law 
in mind, if we have determined the species of the un- 
changed felspar, we may usually determine the other 
with a high degree of probability. 
(3) The chemical and physical characteristics of felspars 

have been already noted as above. 
As regards the origin of felspars : 

They are sometimes clearly the result of wet process ; 
evidence of which is their appearance in veins and 
clefts, also the pseudomorphs which we find after 
leucite, analcime, laumontite, &c. 

Sometimes metamorphic, for Daubree succeeded in pro- 
ducing sanidine-like crystals by subjecting obsidian to 
the influence of overheated steam. 

And sometimes plutonic, as is proved by the presence of 

felspars in lavas and many other rocks of undoubted 

igneous origin, as also in the slags of smelting furnaces. 

Finally, some are the result of process of sublimation. 

Thus, crystals of felspar have been found in blown-out 

furnaces, and, reasoning from analogy, we may suppose 

the same process to have taken place in nature. 

9. Kaolin may be put as an appendix to the felspar group, 

as it is a product of the disintegration of orthoclase, albite, 

and other felspars. Its chemical formula may be stated 

as AJSi + 2H or Al 3 Si 4 + 6H. Occasionally kaolin is the 

result of the decomposition of whole rock masses (granite 

of St. Stephen's in Cornwall, gneiss of St. Yricux, near 



14 MINERALS. 

Limoges, graimlite near Passau). It occurs only in primary 
formations. On the other hand, the clays (which, in a che- 
mical point of view, may be called impure kaolin) always 
occur in secondary formations. 

More or less allied to kaolin are the following minerals, 
all of whose composition is, however, more or less indefi- 
nite, viz. lithomarye, myelin, halloysite, bole or bolus, rock- 
soap, and agalmatolite. These sometimes occur as separate 
independent mineral deposits, but principally are found filling 
cavities and nests in various rocks, in which latter case they 
are to be regarded as products of exfiltration from those rocks. 
Chemically they are all hydrous aluminous silicates, and in 
appearance may easily be mistaken for soapstone, talc, &c. 

Leucite and Nepheline Group. 

The minerals of this group, which in many respects are 
closely allied to the felspars, are without doubt of contem- 
poraneous origin with the volcanic (or plutonic) rocks, in 
which they occur as essential constituents. They are, there- 
fore, almost always, if not always, igneous products. "We 
do not, however, mean to dispute the possibility of some 
having arisen by wet process. The most questionable of all 
in respect of origin is probably lapis lazuli. 

10. Sodalite. Monometric in dodecahedrons ; cleavage, 
accordingly, also massive. Fracture conchoidal to uneven. 
H. r= 5-5-6. S.G. =2-26. Colour yellowish, greenish- 
white, greenish-grey, and blue. Lustre on crystal sur- 
faces vitreous ; on fracture surfaces resinous. Translucent. 
Cp. = Na s Si + SAlSi + NaCl. Bp. fuses, with more or less 
difficulty, to a colourless glass, sometimes with intumescence. 
Gelatinises with muriatic and nitric acids. Sodalite is an 
essential constituent of miascite, and an accessory in other 
igneous rocks (dolerite at the Kaiserstuhl) . 



LEUC1TE AXD NEPHELINE. 15 

11. Lapis lazuli (ultramarine). Monometric in dodeca- 
hedrons ; cleavage accordingly, usually massive. H. = 5*5. 
S. G. = 2'4. Colour azure-blue. Lustre glassy, resinous. 
Translucent at the edges to opaque. Cp. a silicate of Al 
with Na and Ca, containing also NaS. Bp. loses its co- 
lour and fuses to a white vesicular glass. Gelatinises with 
muriatic acid, and evolves HS. Lapis lazuli is found as an 
accessory in granite, limestone, and dolomite. 

12. Haiiyne. Monometric in dodecahedrons ; cleavage, ac- 
cordingly, usually in crystalline grains. H.= 5'5. S. G. 
= 2 '4 2 '5. Colour blue, rarely green or red. Lustre vi- 
treous to resinous ; semi-transparent to translucent. Cp.= 
Na 3 Si + 3AlSi + 2CaS. Bp. decrepitates violently, and fuses 
to a blue-green vesicular glass. Gelatinises with muriatic 
acid. It occurs in single crystals imbedded in the lavas of 
active volcanoes (Volturara, near Melfi), or in the basaltic 
lavas of extinct volcanoes (Niedermendig, on the Rhine), in 
which latter it is characteristic as an accessory mineral, and 
occasionally occurs in such quantity as to have given rise to 
the name of Hauynophyre for those rocks. 

Nosean is very similar to haiiyne in its mineralogical 
character and geological habitat, usually yellowish-grey or 
greyish- white. In Brava, one of the Cape Verde Islands, 
there occurs a porphyry rock, consisting of very numerous 
small crystals of nosean in a felsitic mass. Cp.= Na 3 Si4- 
SAlSi+NaS. 

13. Leucite. Monometric, only known in trapezohedrons 
(embedded). Cleavage cubic, imperfect. Fracture con- 
choidal. H. = 5'5 6. S. G. = 2'48. Colour greyish or 
reddish- white, also ashen-grey. Lustre vitreous, in fracture 
resinous. Semi-transparent to translucent only at the edges ; 
brittle. Cp. = K 3 Si 2 -I- 3AlSi 2 . Bp. unchanged ; with cobalt 
solution coloured a beautiful blue; with borax melts to a 



16 MINERALS. 

clear glass. Gelatinises with muriatic acid. Lencite is a 
frequent and very characteristic constituent of recent ig- 
neous rocks, in which it appears to some extent to be a sub- 
stitute for felspar. It is especially frequent in basaltic lavas 
(leucitophyre), in which it always appears porphyritically 
imbedded. In the older rocks leucite is unknown. 

14. Nepheline (Davyne, Elceolite). Hexagonal. Crystals 
with imperfect basal and prismatic cleavage, or massive. 
Fracture conchoidal to uneven. H.= 5'5 6. S. G. = 2*5 
2*64. Colourless, white and usually crystallised (nephe- 
line), or green, red, brown, and then massive (elaeolite). 
Lustre on crystal surfaces vitreous ; on fracture surfaces 
pre-eminently resinous. Transparent to translucent at the 
edges. Cp. = (]STaK) 2 Si + 2A1S1 = 44Si + 33A1 + IGlSTa + 5K 
(with small quantities of Fe and Ca). Davyne, which is 
very similar, both chemically and mineralogically, contains, 
in addition to the above, some Cl and C. Bp. nepheline fuses 
with difficulty, and elseolite readily to a vesicular glass. 
Slowly dissolved in borax and phosphor- salt. The fused 
edges are coloured blue in cobalt solution. Gelatinises with 
muriatic acid. It occurs in geodic cavities of lavas, and as 
an accessory constituent of dolerite and basalt. In these 
rocks it sometimes forms a complete substitute for the fel- 
spar, producing nepheline rock. Finally it appears as an 
essential constituent of some of the older plutonic rocks 
(miascite, zirconsyenite) . In dolerite it may be recognised 
by its forming short thick columns, whilst the apatite, which 
is associated with it in those rocks, assumes the form of 
acicular hexagonal columns. 

(&) AUGITE SECTION. 

15. Hornblende (Amphibole). Monoclinic. Crystallised or 
massive, in stalklike or granular aggregates. Cleava ge pris- 



LEUCITE GROUP AUGITE. 17 

matic, very perfect ; in other directions imperfect. Fracture 
uneven. H. = 5 6. S.G.=2'9 3*4. Colour passing from 
white through various shades of green and brown to black. 
Streak either colourless or lighter than the colour of the 
mineral. Lustre vitreous, on cleavage surfaces mother-of- 
pearl ; the fibrous varieties silky. All degrees of trans- 
parency to the opaque. Cp. variable. We may give as a 
normal formula, R 3 Si' 2 + RSi, in which B = Mg, Ca, and Fe, 
and Si is sometimes partially replaced by Al. Bp. these 
minerals usually fuse, with intumescence, to a grey, greenish, 
or black glass, and the more readily the more iron they con- 
tain. The varieties richest in iron are partially decomposed 
by muriatic acid ; other varieties are little affected by that 
acid. 

(a) Tremolite (Grammatite, Calamite). Of light colour, 
semi-translucent. Iron not an essential ingredient. 
Cp. = Mg'S'i 2 + CaSi=60Si + 27Mg + 12Ca. Usually 
imbedded in granular limestones and dolomites, in the 
form of long columnar crystals, or long stalklike or 
fibrous masses. 

(6) Actinolite (Strahlstein, Glassy Actinolite). Colour green. 
Cp. like tremolite. Occurs as an accessory in talc- 
schist, chlorite-schist, &c. also as an independent rock 
(actinolite-schist) . 

(c) Hornblende (proper). Colour dark-green or black; 
opaque. Cp. rich in iron and alumina. Forms an 
independent rock of itself, or occurs as an essential 
constituent of many compound rocks (syenite, diorite, 
many kinds of gneiss and porphyry). Occurs in the 
form of very perfect brownish-black crystals, imbedded 
in basaltic and trachytic rocks. A variety of the 
mineral is termed gamsigradite, and forms an essential 

constituent of the rock timazite. 
C 



18 MINERALS. 

(d) Uralite has the same cleavage, structure, and composition 

as hornblende, but the exterior form of augite. Crystals 
of this mineral occur in many greenstones (uralite- 
porphyries). (Predazzo.) 

(e) Asbestus and amianthus are fibrous varieties of tremolite 

and actinolite. In the variety known as Mountain 
leather the fibres are closely interlaced, or woven like 
felt. These minerals fill cavities and clefts in lime- 
stone and serpentine. 

(/) Nephrite and Jade may be here added. They consist of 
a compact white or light-green translucent mass, with 
splintery fracture. Cp. very variable, sometimes that 
of tremolite. It is not a rigidly- defined mineral ; 
forms independent layers as deposits between talcose 
rocks (in Turkey, New Zealand, &c.). 

16. Pyroxene (Augite). Monoclinic. In crystals imbedded 
or attached, or in stalklike, scaly, or granular masses. 
Cleavage prismatic, but usually less perfect than hornblende. 
Fracture conchoidal to uneven. H.=5 6. S.Gr.^3'2 3'5. 
Rarely colourless. Colour usually grey, green, or black. Lustre 
vitreous, sometimes mother-of-pearl. All degrees of trans- 
parency. Cp.=R, 3 Si 2 , but very variable. Si partly replaced 
by Al ; R. Ca, Mg, Fe, Mn. Bp. the pyroxenes fuse (some 
quietly, others with some effervescence) to a white, grey, 
green, or black glass. Usually they are with difficulty re- 
ducible by microcosmic salt ; those that contain Al almost not 
at all. Almost all exhibit the reaction for iron, the white 
and light-coloured varieties manganese. Imperfectly decom- 
posed by acids. The following mineralogical varieties are 
distinguished : 

(a.) Diopside. Light- coloured, transparent and translucent 
varieties, and 

(5) Salite. Green, translucent only at the edges ; usually 



AUGITE SECTION. 19 

foliated. This and the last are without much geological 
importance. A sahlite, termed malakolite, is however 
found separately imbedded in the granular limestone. 

(c) Augite. Green to black, opaque. Occurs as an essential 

ingredient in basalt, dolerite, diabase, and many lavas. 
Frequently in the form of perfect crystals porphyriti- 
cally imbedded. Also found in meteoric stones. 

(d) Omphazite. Grass-green, always accompanied by garnet, 

and together with it forming eklogite. 

(e) Hypersthene (Paulite). Reddish-brown, greenish-black, 

or black, with metallic mother-of-pearl lustre on the 
faces of most perfect cleavage, and sometimes a change 
of colours showing a copper-red tinge. Lustre other- 
wise vitreous or resinous. In thin lamellce translucent. 
Cp. very poor in lime, rich in iron and manganese. 
Hypersthene is an essential constituent of the rock 
hypersthenite (Penig in Saxony, Isle of Skye, Southern 
Tyrol). Otherwise it is usually an accessory, and is 
especially frequent in gabbro. 

Appendix to Pyroxene. 

Diallage (Smaragdite), which is an essential consti- 
tuent of many gabbro rocks, is only a peculiar variety 
of pyroxene or hornblende, or perhaps a mixture of 
both. 

The following are hydrous products of the decomposition of 
pyroxene : 

Schiller spar. An essential constituent of schiller rock 
(Baste, in the Harz), accessory in serpentine. 

Palagonite. The principal ingredient of the tufa of 
that name (Sicily, Nassau). 

Green Earth. Frequent in vesicular cavities of 
amygdaloids and in basaltic tufas. 
c 2 



20 MINERALS. 

The distinction between hornblende and pyroxene is ex- 
tremely important lithologically, but is often attended with 
considerable difficulty. Some assistance may be derived from 
the following remarks : 

(a) As to Grystallograptiic Differences. Only recognisable in 
cases of granular texture, where the crystals are tolerably 
perfect. One of the most essential and best-marked 
differences consists in the different angles of the 
cleavage prisms of the two minerals (and those are 
usually identical with the angles of the exterior faces 
of the crystal.) In hornblende the larger angle of the 
prism is 124 30' (giving a complement of 55 30') ; 
in pyroxene the angles are 87 5' to 92 55'. 

(/3) Differences of Par agenesis. Rocks containing free quartz, 
felspars rich in silica (such as orthoclase and albite), 
or potash-mica as essential constituents, seldom 
likewise contain augitic minerals, but if the latter 
occur, they are almost invariably hornblende, and not 
pyroxene. In pyroxenic rocks, quartz especially is 
very rarely found, and if present is only accessory 
(eklogite, hypersthenite). On the other hand, labra- 
dorite and magnesian micas are very frequent in such 
rocks, though not exclusively there found. 

Pistacite and pyrites are more frequent accessories 
in hornblendic than pyroxenic rocks. The pistacite is 
found adhering to the surfaces of clefts, or in geodic 
cavities, and would appear in most cases to be a pro- 
duct of the decomposition of amphibolite. 

Leucite and olivine are characteristic as accessory 
minerals in pyroxenic rocks. 

As a very general rule, we may characterise horn- 
blende as the constituent of the plutonic, pyroxene as 



AUGITE SECTION. 21 

that of the volcanic igneous rocks. Nevertheless, 
sometimes both are found together in the same rock 
(basalt, omphacite, trachyte of Etna). In this latter 
case the pyroxene is the older formation of the two, 
i.e. it has cooled and become solid more rapidly than 
the hornblende. 

(y) The chemical differences between pyroxene and hornblende 
are not marked. It would appear as if one or the other 
might have resulted from the same identical mass ac- 
cording to the conditions under which it cooled and 
solidified. The origin both of hornblende and of 
pyroxene may be of various kinds. 

The possibility of their formation by wet process 
during the development or the transmutation of a 
rock's mass has been proved by Daubree, who actually 
produced diopside by subjecting glass to the influence 
of the thermal waters of Plombieres. 

Many of the crystals which are found disseminated 
in limestone rocks would appear to be the result of 
metamorphosis (Pargas, Tyrol). 

Again, both these minerals may be products of sub- 
limation (Elie de Beaumont, Sacchi), or they may be 
simple products of igneous action, since we find in the 
slags of smelting furnaces products of precisely similar 
form and composition. 

17. Spodumene (Triphane). Monoclinic, isomorphous with 
pyroxene; crystallised or massive in broad fibrous or scaly 
masses. Cleavage orthodiagonal and prismatic. Fracture 
uneven. H.=6'5 7 S.G. = 3'1 3'2. Lustre vitreous, with 
mother-of-pearl lustre on the cleavage surfaces. Colour 
greenish-grey to apple-green. Translucent, but frequently 
only at the edges. Cp. = Li 3 Si 2 + 4AlSi 2 frequently with some 
Na, K, or Ca. Bp. intumescent ; colours the flame red, but 



22 MINERALS. 

weakly and transitorily. Fuses easily to a clear glass. When 
mixed with Ca F and KS 2 , it gives a purple-red flame. Is 
not affected by acids. Spodumene is found imbedded in gra- 
nite (Uto in Sweden ; Killiney Bay, Ireland ; Peterhead, 
Scotland). It also occurs in the quartz veins of mica-schist 
(Massachusetts) . 

Killinite is a product of the weathering or decomposition of 
spodumene. 

(c) MICA SECTION. 

This is a section of minerals distinguished by their pre- 
eminent foliation (basal cleavage) to a degree not known in any 
other mineral. As regards origin, they are in part purely 
plutonic, being found even in the most recent igneous rocks. In 
part however, they are products of wet processes, and we find 
pseudomorphs after felspar, tourmaline, and other minerals. 

18- Potash-Mica (Phengite, Muscovite, Binaxial Mica), 
Trimetric with monoclinic aspect. The crystals usually appear 
as rhombic or hexagonal plates. Sectile, and its thin laminse 
elastic. H.=2 2'5. S.G.=275 31. Colourless, frequently 
white, and various shades of yellow, green, or red. Light 
colours are characteristic. Metallic mother-of-pearl lustre. 
Transparent to translucent. Optically very distinctly binaxial ; 
the angle of the optical axes =45 75. Cp. variable average 
formula==mAlSi + KSi ; in which formula ra=2, 3 or 4. A 
portion of the Al may be replaced by Fe, Mn, Cr ; a portion 
of the K by Fe and Mn. Strange to say no Ca is to be found 
in any species of mica. The K is usually =8 9 per cent. 
There is usually from 1 5 per cent, of water and some fluorine. 

Bp. fuses, with more or less readiness, to a cloudy glass or 
a white enamel. Not affected by muriatic or sulphuric acid. 

Potash-mica is an essential ingredient of many rocks, and 
especially characteristic for the older plutonic or metamor- 



MICA SECTION. 23 

plilc rocks, thus for many kinds of granite, gneiss, and mica- 
schist. 

Damourite, Margarodite, and other similar minerals of very 
limited frequency, are, in part at least, products of transmu- 
tation of potash-mica. They occasion a transition to the 
chlorites. The same may be said of Sericite, a green mineral, 
of silky lustre, which is said to form the base of several crys- 
talline schists and clay-slates ; but it is not .yet free from 
doubt whether or not sericite is entitled to be regarded as an 
independent mineral. List gives the following account of 
sericite H.=l. S.G.=2'89. Foliated in one direction ; planes 
undulated. Lustre silky. Colour greenish or yellowish- 
white. 

19. Lithia-Mica (Lepidolite, Lithionite). Trimetric, corre- 
sponds with potash-mica in many crystallographic and phy- 
sical properties, except that its colour is frequently red. 
H. = 2'5 4. S.G.=2'84 3. The angle of the optical axes 
= 70 78. 

Cp. very variable, may be generally expressed by the 
formula mRSi+7&RSi; m = w=l; or ra=2, n=3 ; or some- 
times m=3, n=.2. Again, a part of the bases, as well as of the 
acids, are compounds of fluorine, not oxygen. The content of 
lithia is usually 2 5 per cent., and of fluorine 2 10. Bp. 
fuses very readily, with efflorescence to a colourless, brown, 
or black glass. The flame is coloured purple-red ; with acids 
it is imperfectly soluble, but completely decomposed. 

Lithia-mica is an essential ingredient of Greisen, very fre- 
quent in some kinds of granite, and in metalliferous veins, 
especially those of tin. In all these cases this mineral is 
usually associated with other fluorides, such as topaz, tourma- 
line, apatite, &c. 

20. Magnesia-Mica (Biotite, Hexagonal or Uniaxial Mica). 
The name of uniaxial mica is now found to be incorrect, as 



24 MINERALS. 

all magnesia-mica is "binaxial, if only slightly. The angle of 
the two axes is for the most part less than 5. Trimetric (?) 
crystals, usually tabular ; usually sectile, and in thin plates, 
elastic. H.=2'5 3. S.G. -- 27 31. Green, brown, black, in 
general colours usually dark. Metallic mother-of-pearl lustre. 
Translucent to opaque. Cp. very variable; chiefly =AlSi + 
K, 3 Si, in which Al is in part replaced by Fe, and R--Mg, K, 
Fe. The Mg=9 25 per cent. Some fluorine, chlorine, and 
water likewise enter into the composition. Bp. fuses with 
greater difficulty than the before-mentioned species of mica, to 
a grey or black glass. It is little attacked by muriatic acid ; 
on the other hand, unlike potash-mica, it is completely de- 
composed by concentrated sulphuric acid, leaving a white 
residue of silica. 

The geological area of biotite is far more extensive than 
that of potash-mica, for it is not only found in the older 
plutonic rocks and crystalline schists (granite, porphyry, 
gneiss), but also in more recent and the most recent volcanic 
products (trachyte, basalt, and the corresponding lavas). 

Rubellan and Phlogopite are minerals closely allied to mag- 
nesia-mica, of which rubellan is perhaps only a transformed 
product. 

(d) HYDROUS MAGNESIAN SILICATES (TALC SECTION). 

These have many characteristics and properties in common. 
Some minerals which contain Fe instead of Mg belong to the 
same group. We may make three principal divisions : the 
Chlorites (21), the Serpentines (2225), and the Talcs (26,27). 
The chlorites under certain circumstances may be regarded as 
hydrous mica ; the serpentines and talcs appear chiefly to be 
products of metamorphosis, perhaps occasioned by percolating 
water. The most important species are : 

21. Chlorite (Ripidolite). Ehombohedral ; the crystals 



TALC SKCTIOX. -25 

grouped in the form of comb or botryoidal shape, usually in 
massive, foliated, or scaly aggregates. Cleavage basal, very 
perfect; sectile. Its thin lamellae flexible, but not elastic. 
H.=l 1-5. S.Gr.=2'65 to 2'85. Colour green, in various 
shades. Its crystals are frequently translucent, and of red colour 
when regarded in the direction of thfc principal axis. Streak 
greenish-grey. Lustre mother-of-pearl. Thin laminae trans- 
parent to translucent. Cp.=3R 3 Si-f E 3 Si-f 12H=30 31 Si + 
1419 Al + 32 37 Mg+5 6 Fe. In matrass it gives out 
water. Bp. fuses on charcoal ; with borax it melts and shows 
uhe reaction of iron. Thin laminae are decomposed by concen- 
t rated sulphuric acid. 

Chlorite forms the most important and essential elements 
of chlorite- schist, also of chlorite mica-schist, both frequent in 
the Alps. In the protogine-granite and protogine-gneiss it is 
a substitute for mica. It is also a characteristic constituent 
of diabase, and many kinds of syenite-porphyry (Altenberg in 
Saxony). 

Delessite is a mineral closely allied to chlorite, but richer 
in iron. It is frequent in vesicular cavities of melaphyres. 

Pennine, Ripidolite, and Clinochlore are minerals resembling 
chlorite, but not yet accurately denned. They are of frequent 
occurrence in chloritic schists as essential ingredients. 

Some of the minerals which we have already noticed as 
having arisen from transmutation of augite, such as schiller 
spar, green earth, &c., are externally very similar to chlorite. 

22. Saponite (Soapstone) . Massive, sectile, and very soft. 
S.G.^2'26. Colour white or light grey, yellow or reddish 
brown, dull, with lustrous streak. Greasy feel, not adhesive 
to the tongue. Cp. = 2Mg 3 Si 2 + Al *Si + 10H. In the matrass 
it gives out water and becomes black. Thin laminae melt 
with difficulty at the edges. It is readily and completely 
decomposed with sulphuric acid. 



26 MINERALS. 

Saponite occurs in fissures of serpentine rock (Lizard's 
Point, Cornwall). 

23. Serpentine. Usually compact, sometimes granular or 
fibrous ; in the latter case it is called chrysolite or serpentine- 
asbestus. Fracture conchoidal, flat, or uneven, splintery, 
fine-grained, or of twisted fibres. H.=3 4, rarely 5 ; S.G.= 
2 '2 2 '6. Bright coloured and translucent varieties are termed 
precious serpentines to distinguish them from the ordinary 
serpentine, which is usually of dark colour green, red, 
or brown. Cp.=the general formula Mg 9 Si 4 H (i =43 Si + 
42 Mg + 12 H, with a trifling percentage of Al and Fe. In 
matrass gives out water and becomes darker in colour. Bp. 
almost infusible, exhibits the reaction of iron ; easily soluble 
in borax, in microcosmic salt with effervescence. When 
powdered, soluble in muriatic acid, and still more readily 
in sulphuric acid. 

Serpentine is found disseminated in rocks, usually massive, 
sometimes in broken masses, plates, and veins. It likewise 
forms a rock of itself. 

The right of serpentine to the character of an independent 
mineral is open to doubt, as it frequently appears to be only 
a pseudomorph of other minerals, e. g. hornblende, augite, 
garnet, spinel, &c. The rock serpentine also appears to be 
usually, if not always, a product of transmutation derived 
from other rocks, such as granite, gneiss, gabbro, chlorite- 
schist, &c. ; and only to resemble the mineral, not to con- 
stitute, strictly speaking, an aggregate of it. (Yide post, 
p. 314.) 

24. Ottrelite. In small thin hexagonal or rounded laminae ; 
cleavage parallel to the lateral faces. Hard; is capable of 
scratching glass. S.Gr. =4'4. Greenish grey to blackish-green. 
Lustre vitreous; translucent. Cp. = (Fe,Mn) 3 Si 2 + 2AlSi + 
3H. In matrass gives out water. Bp. fuses with difficulty 



TALC SECTION. 27 

at the edges to a black magnetic globule ; with borax, iron 
reaction ; with soda, that of manganese. 

Ottrelite is found disseminated in various kinds of clay- 
slate, which have received the name of Ottrelite Slate (Lux- 
embourg). 

25. Glauconite. Small, round, dark-green grains, which 
when recently exposed are frequently very soft, but in time 
assume about the hardness of gypsum. S.G.=2'29 2'35. 
Cp.=a hydrous silicate of Fe and K (5 10 per cent. K), 
moreover Al and small quantities of Ca and Mg. 

Glauconite is found in the form of grains or nuclei of 
minute fossils (Foraminifera) imbedded in clay-marl and 
sandstone rocks. Very characteristic for rocks of the Chalk 
formation (Upper Greensand, Isle of Wight; Chalk of Calais). 
Occurs also in other sedimentary formations (Muschelkalk of 
Berlin ; Calcaire grossier, Paris ; Browncoal Sandstone of 
the North-eastern Alps). 

26. Talc. Trimetric (?) ; rarely crystallised, usually mas- 
sive, in granular, foliated or scaly aggregates. Cleavage basal, 
very perfect. Very sectile with greasy feel. Thin laminae 
flexible, but not elastic. H.=l 1-5. S.G. = 2'56 2-8. 
Colour white, grey, and green, in various shades. Lustre 
mother-of-pearl, or resinous. Translucent to opaque. Opti- 
cally binaxial. Cp. = Mg 6 S> + 2H=62 Si + 32'9 Mg-f 4'9 H. 
The Mg is partly replaced by Fe. Bp. shines brightly and 
loses its colour ; exfoliates ; becomes hard ; does not fuse. 
If heated with cobalt solution, becomes pale-red. Is not at- 
tacked by acids. 

Varieties especially noticeable are : 

(a) Foliated Talc. The purest crystalline talc. 
(6) Steatite. Amorphous. Frequently pseudomorphous after 
other minerals. Decomposes with boiling sulphuric acid. 



28 MINERALS. 

Talc is a very widely diffused mineral. Talc-schist and 
many beds of rock in the regions of crystalline schists con- 
sist almost exclusively of this mineral. Talc-mica-schist, 
protogine, and some sandstones contain it as an essential 
ingredient. 

27. Meerschaum. Massive and in nodules. Fracture flat 
conchoidal, and fine-grained, earthy; sectile. H. = 2 2 '5. 
S.G.=0'8 1. Colour yellowish or greyish- white, dull. 
Streak little lustrous. Opaque. Greasy feel ; adhering 
strongly to the tongue. Cp. (probably) MgSi + H, usually 
with some C. Bp. contracts, becomes hard, and fuses at the 
edges to a white enamel. 

Forms separate beds, which are the result of a process of 
transmutation, probably of Magnesite. 

(e) ZEOLITE SECTION (NON-MAGNESIAN HYDROUS SILICATES.) 

The minerals which are grouped under the name of Zeolites 
are an extensive family of the silicates, having both as to che- 
mical composition and crystallographic form much in common 
with the Felspar group, as well as with the Augite and the An- 
dalusite groups but their chief distinguishing feature is that 
they invariably contain a large proportion of water, varying 
from 4 22 per cent. 

The following properties are common to all zeolites. Before 
the blowpipe they froth up and melt to a glass, which 
owing to the many bubbles never becomes very clear or trans- 
parent. They are all decomposed by muriatic acid, under 
which process the Si is precipitated to a gelatinous or slimy 
mass. Again, they all have a colourless streak, which circum- 
stance is owing to the small proportion of colouring oxides 
(not above 2 per cent.) which they contain. 

The geological character of the zeolites is very uniform. 
They are principally found in the volcanic rocks. They are 



ZEOLITE SECTION. 29 

either found in the vesicular cavities, veins and fissures of 
those rocks in the form of crystals and foliated and radiated 
masses, or they sometimes form an essential ingredient of the 
rock's mass (in basalt, phonolite). In either case they are 
not original products, i. e. not of contemporaneous formation 
with the rock in which they are found ; they are products of 
exfiltration or of the internal decomposition and transmutation 
of the mother rock. It is interesting to notice with reference 
to those zeolites which are the products of what we have 
termed exfiltration, that Daubree has shown them not to be 
simple deposits of substances held in solution by the per- 
colated water to which they owe their origin, but rather 
products of the chemical action of that water at a high 
degree of temperature on a portion of the rock's mass which 
had already oozed out ; and thus that the same rill of water 
percolating through different rocks will produce different 
species of zeolite. As regards zeolite forming part of the 
composition of the rock's mass, this is so frequently the case 
in basalt, that it has recently been put forth as a universal 
rule that no rnr.k can be a genuine basalt without zeolite. 
Nevertheless we think this assertion too general, and it is 
possible that nepheline, which enters largely into the com- 
position of basalts, may by reason of its great solubility 
in muriatic acid, have been sometimes mistaken for zeolite. 
Zeolites are seldom found in metalliferous veins, or in the 
fissures of the older plutonic rocks. 

The most convenient arrangement of the individual species 
for our present purpose will be the crystallographic. We 
begin with 

The Monometric Zeolites. 

28. Analcime. Usually in trapezohedrons ; more rarely a 
combination of these with the cube. The crystals usually 



30 MINERALS. 

found grouped together in geodic cavities. Sometimes mas- 
sive, granular. Cleavage cubal, imperfect. Fracture uneven. 
H. 5'5. S.G. = 2'1. Colourless, white to grey, or flesh-red. 
Lustre vitreous. Transparent to translucent at the edges 
only. Cp. =JSTa3Si 2 + 3AlSi 2 + 6H. 

Analcime is found in geodic cavities of basaltic rocks 
(Giant's Causeway, Ireland ; Dumbartonshire ; Seisser Alp) ; 
in metalliferous veins (Kongsberg ; Andreasberg in the Harz) ; 
and as a recent formation at the mouth of springs (Plom- 
bieres). It is especially frequent in the old dolomitic lavas of 
the Cyclopean Islands near Sicily, and those have been named 
Analcymite accordingly. The observer must avoid confound- 
ing the crystals of analcime with those of leucite. 

29. Apophyllite (Ichthyophthalmite, Albine). Crystals py- 
ramidal, columnar, or tabular. Usually grouped together in 
geodes ; occasionally in scaly aggregates. Cleavage basal, per- 
fect. Fracture uneven. H.=4'5 5. S.G-. = 2'33. , Colour- 
less, or yellow, greyish, or reddish- white. Lustre vitreous, 
on the cleavage surfaces mother-of-pearl. Transparent to 
translucent at the edges. Cp. -8CaSi-|-KSi 2 + 16H, with 
sometimes 1 per cent, of fluorine. 

Apophyllite is found in the geodic cavities of volcanic rocks 
(Iceland, Faroe, Fassa Thai) in metalliferous veins (at Utoe in ' 
Sweden, at Andreasberg, and in the Bannat associated with 
wollastonite). In the Tertiary limestone near intruded basaltic 
rocks at Puy de la Piquette, in Auvergne. Finally as a recent 
deposit from spring water at Plombieres. 

Hexagonal Zeolites. 

30. Chabasite (Phacolite). Rhombohedral. Crystals often 
of twin growth. Cleavage rhombohedral. Fracture uneven. 
H.=4 4-5 S.G.=2-08 2-17. Colourless, white, or red- 



ZEOLITE SECTION. 31 

dish. Lustre vitreous. Transparent to translucent. Cp.=. 
(Ca,Na,K)3'Si 2 + 3AlSi 2 + 18H. 

It occurs in geodes of volcanic rocks (Faroe, Fassa Thai, 
Giant's Causeway) ; in syenite (Massachusetts) ; ^in gneiss 
(Connecticut). 

Trimetric Zeolites. 

31. Prehnite. Crystals tabular or short columnar. Grouped 
in geodes in fan-shaped or spheroidal aggregates. Cleavage 
basal, perfect. H. = 6 67. S.G.=2'8 2'95. Earely colour- 
less, usually green. Lustre vitreous ; on the cleavage surfaces, 
mother-of-pearl lustre. Transparent to translucent at edges 
only. Cp. Ca 2 Si + AlS'i + H, frequently with some Fe. 

Occurs in basaltic amygdaloids (Fassa Thai) ; in the trap 
rocks of Dumbarton. 

32. Thomsonite (Comptonite) . In geodes, the crystals in 
sheaves or fan-shaped groups, or in fibrous aggregates. Cleav- 
age, according to the brachy- and macro-diagonal, almost 
equally perfect. Fracture uneven. H. = 5 5*5. S.G.=2'35 
2 '38. Colour white. Lustre vitreous, sometimes mother-of- 
pearl. Translucent, but usually clouded. Cp. = (Ca v N"a) a Si + 
3AlSi + 7H. 

Thomsonite occurs in amygdaloids at Kilpatrick, in Dum- 
bartonshire, and Lochwinnock, in Renfrewshire, in the 
vesicular cavities of Vesuvian lavas, in the analcimite and 
phonolite of Bohemia. 

33. Natrolite (Soda-Mesotype) . Crystals usually thin, co- 
lumnar, acicular, or capillary. In geodes, also in bunches or 
reniform masses. Cleavage prismatic, perfect. H.=5 5*5. 
S.G.-=2-17 2-24. Colourless, greyish-yellow or reddish- 
white. Lustre vitreous, occasionally mother-of-pearl. Trans- 
lucent, or only at the edges. Cp. = NaSi * AISi -f- 2H, occa- 
sionally a small quantity of Fe. 



32 MINERALS. 

Natrolite occurs in vesicular cavities of basaltic and phono- 
lite rocks (Kilmalcolm in Renfrewshire, Aussig in Bohemia) . 

34. Pliillipsite (Lime-Harmotome) . Columnar crystals, 
sometimes long and sometimes short, frequently twin, growth 
cross-shaped. Cleavage brachy- and macro- diagonal. EL 
4 4'5. S.Gr. = 2'2. Colourless, white, yellowish or reddish. 
Lustre vitreous. Transparent to translucent at the edges 
only. Cp. = (Ca,K)Si+AlS> + 5H. 

Phillipsite is found in the basaltic lavas of Capo di Bove 
near Rome, County Antrim, in Ireland, &c. 

35. Harmotome (Baryt-harmotome). Columnar crystals 
almost always twins, shaped in form of a cross. Cleav- 
age imperfect, the brachydiagonal more perfect than the 
macrodiagonal. H.=4'5. S.G.=2'39 2*5. Colourless, or 
different shades of white. Lustre vitreous, little translucent. 
Cp.=BaSi+AlSi 2 + 5H, with some K and Ca. 

Harmotome occurs in the metalliferous veins of Andreas- 
berg, in nodules of agate from the melaphyre of Oberstein, 
Zweibrucken, under like circumstances in Dumbartonshire, 
where its crystals are simple. 

Monoclinic Zeolites. 

36. Laumontite (Laumonite). The crystals usually in colum- 
nar combinations, also in granular and fibrous masses. Cleav- 
age prismatic, perfect ; very friable and brittle. H. = 3'5 4. 
S.G.=2'29 2*36. Colour yellowish, or greyish- white, also 
reddish. Lustre vitreous, on the cleavage surfaces mother-of- 
pearl. Transparent to translucent on the edges only. Cp.= 
Ca 3 Si 2 + 3AlSi 2 + 12H. It loses a portion of its water very 
quickly on exposure, and then falls to powder. 

Laumontite is found in vesicular cavities of basaltic rocks 
(Dumbartonshire, Faroe), in clefts and fissures of syenite 
(Dresden), or quartz-porphyry (Botzen). 



ZEOLITE SECTION. 33 

37. Scolecite (Lime-Mesotype) . Crystals long or short prisms 
or acicular ; also massive, radiated, and fibrous. Cleavage 
prismatic, tolerably perfect. H. = 5 5'5. S.G.=2'2 27. 
Colourless, greyish, yellowish, or reddish- white. Lustre 
vitreous, the fibrous clusters silky. Transparent to trans- 
lucent at the edges only. Cp. = CaSi + AlSi + 3H. 

Scolecite occurs in the vesicular cavities of basaltic rocks 
(Auvergne, Staffa), or in the fissures of the same rocks (Kil 
patrick hills). t 

38. Heulandite (Foliated Zeolite, Stilbite, in part). Crystals 
usually tabular, rarely prismatic, either single or clustered in 
geodes, also massive, in radiated, foliated, or globular aggre- 
gates. Cleavage clinodiagonal, very perfect. H.=3'5 4. 
S.Gr.=2'2. Colourless, white, usually red to brown. Lustre 
vitreous, on the cleavage surfaces, mother-of-pearl. Transpa- 
rent to translucent at the edges only. Cp. =CaSi + AlSi 3 + 5H. 

Heulandite occurs frequently in the vesicular cavities of 
basaltic rocks (Faroe, Iceland, Skye, Fassa Valley) ; rare in 
metalliferous veins (Andreasberg). 

39. Stilbite (Desmine, Radiated Zeolite). Its monoclinic 
character is questionable. The crystals are broad prisms, 
frequently clustered into sheaves or bundles ; also massive and 
fibrous aggregates. Cleavage brachydiagonal, very perfect, 
macrodiagonal imperfect. H.=3'5 4. S.G. = 2'1 2'2. Co- 
lourless, white, grey, yellow, or red. Lustre vitreous, on the 
most perfect cleavage surfaces, mother-of-pearl lustre. Trans- 
lucent, perfect or only on the edges. Cp. - CaSi + AISi 3 + 6H. 

Stilbite is a frequent inhabitant of vesicular cavities or 
fissures of volcanic rocks (Fassa-Thal, Faroe, Iceland) also 
occurs in metalliferous veins (Andreasberg, Kongsberg). 

40. Smitlisonite (Hydrous Silicate of Zinc, Galmey, in part) 
may be added here by way of appendix, although geologically 
it is very far removed from the zeolites, since chemically it 



34 MINERALS. 

agrees with them in being a hydrous silicate free from 
magnesia. 

It crystallises trimetrically, hemimorph. The crystals are 
nsnally small, tabular, and prismatic, independent or in geodes, 
frequently grouped in fan-like, grape-like, botryoidal, or reni- 
form clusters ; also fine fibrous to felt- like varieties occur. 
Cleavage prismatic, very perfect, macro- domatic perfect. Frac- 
ture uneven. H.=4'5 5. S.G. = 3'16 3'9. Colourless, 
white and variously coloured (but always light coloured). 
Lustre on crystal surfaces vitreous. Semi-transparent to 
opaque. Cp.=2Zn 3 Si + 3H. When heated in matrass gives 
out water. Bp. decrepitates a little, shows green phospho- 
rescent light, but does not melt. Gelatinises with acid. 

Smithsonite takes no essential part in the composition of 
rocks, but both alone and with other zinc-ores and galena forms 
separate beds of ore of considerable extent. These ores are 
usually associated with dolomites and limestones (Raibl and 
Bleiberg in Carinthia, Aachen, Tarnowitz in Silesia, Mendip 
hills). Smithsonite occurs in veins of lead-ore at Matlock in 
Derbyshire, and many other English localities. 

(/) ANDALUSITE SECTION. 

With respect to the minerals grouped under this head, 
we must remark that they are allied together more by 
their chemical and physical properties than their geological 
affinities. 

41. Andalusite (Chiastol/ie, Hohlspath). Trimetric. The 
crystals are usually combinations of the prism and base, hence 
columnar, attached, also imbedded ; also in radiated, fibrous, 
and granular clusters. Cleavage prismatic, imperfect. Frac- 
ture uneven and splintery. H. - 7*5. S.G. - 3'1 3 P 2. Colour 
grey, greenish, or reddish-^ ; ev. Lustre vitreous, usually weak. 
Barely transparent, and in that case showing trichroism ; 



ANDALUSITE SECTION. 35 

usually translucent, or translucent only at the edges. [The 
variety chiastolite fluctuates in hardness between 3 and 7'5. 
This difference is attributable to foreign substances contained 
in its crystals. These foreign substances are arranged in some 
sort symmetrically about the edges and axis so as to give a tes- 
selated appearance in the section. The crystals are mostly 
twins or fourfold.] Cp.= Al 3 fii 2 , sometimes Al 4 Si 3 , usually 
with some Fe and Mn. Bp. infusible. When reduced to 
powder, fuses with difficulty in borax to a transparent colour- 
less glass ; with cobalt solution coloured blue. Not affected 
by acids. 

Andalusite occurs as an accessory in granite and crystalline 
schists (gneiss, mica-schist), Devonshire and Aberdeenshire. 
The variety chiastolite occurs exclusively in clay-slate, and 
usually in the neighbourhood of granites or other igneous 
rocks. It probably is the product of a metamorphosis result- 
ing from percolated water. 

42. Topaz. Trimetric. Crystals sometimes hemimorphous, 
always prismatic. Single crystals attached or imbedded, or 
clusters incrusted in geodes ; also coarse or fine-grained 
masses. Cleavage basal, very perfect. Fracture conchoidal 
to uneven. H. = 8. S.G.=3'4 3*6. Colourless and transpa- 
rent, but usually yellow, red, or blue. Lustre vitreous. Trans- 
parent to translucent at the edges only. Cp. = 5Al 3 Si 2 + 
(3AlF 3 + 2SiF 3 ) shows reaction of fluorine. Bp. infusible, 
but soluble in microcosmic salt, leaving a skeleton of silica. 
Not affected by muriatic acid. With sulphuric acid, some 
hydrofluoric acid is formed. 

Pycnite is a fibrous variety of topaz. 

Topaz is an essential constituent of topaz-rock, an accessory 
of granite (imbedded, or incrusting geodic cavities) : Mourn e 
in Ireland, Mursinsk in Siberia, Greifenstein in Saxony. Very 

frequently associated with other minerals which contain fluo- 

D 2 



36 MINERALS. 

rine, and with beryl and tin ore. Also in separate localities, 
associated with the like minerals (Cornwall, Saxony). 

Although the topaz crystals which are found imbedded in 
granite appear to be of simultaneous formation with that rock, 
and therefore of plutonic origin, Daubree has succeeded in 
producing topaz by subjecting alumina to the action of fluoride 
of silicon. 

43. Staurotide (Staurolite). Trimetric. Crystals always 
imbedded, prismatic, frequently cruciform. Cleavage brachy- 
diagonal, perfect. Fracture conchoidal to uneven. H. = 7 7'5. 
S.Gr.=3'5 3*7. Deep red to blackish-brown. Lustre vitre- 
ous. Translucent to opaque. Cp. variable =(AlFe) 2 Si, or 
R, 3 Si 2 , or R 5 Si 4 . Bp. infusible. With difficulty soluble in 
borax and microcosmic salt. Not affected by muriatic acid. 

Staurotide occurs in association, sometimes twin growth, 
with the next named species ; accessory in mica- schist and 
gneiss (Switzerland, Tyrol, Brittany). 

44. Ky unite (Disthene,Rhoeiizite'). Triclinic. Crystals usually 
long and broad-shaped (bladed), without terminal faces, fre- 
quently in twins ; imbedded singly or grouped in fibrous 
masses. Cleavage prismatic, very perfect, brittle. H.=6 7'2. 
S.G. =3*56 3'67. Colourless or common blue. Lustre vitre- 
ous, on the most perfect cleavage planes, mother-of-pearl. 
Transparent to translucent on the edges only. Cp. = Al 3 Si 2 , 
with little Fe. Bp. infusible ; dark blue if heated with cobalt 
solution. Not affected by acids. 

Kyanite occurs as an accessory ingredient in granulite, also 
in gneiss and mica-schist similarly to staurotide. 

45. Lievrite (Tlvaite^Jenite) . Trimetric. Crystals long prisms. 
Crystals attached or incrusting geodic cavities ; also massive, 
usually in fibrous, rarely in granular aggregates. The crystals 
usually coated with brown iron-ochre. Cleavage indistinct. 
Fracture conchoidal to uneven. Brittle. H.=5'5 6. S.Gr.=: 



ANDALUSITE SECTION. 37 

3'8 4'2. Colour brownish to greenish-black. Streak black. 
Lustre resinous. Opaque. Cp.=2Fe 3 Si + Ca 3 Si + Fe 2 S'i. Bp. 
fusible to a black magnetic globule; with microcosmic salt 
shows the reaction of iron, and leaves a skeleton of silica. 
With muriatic acid gelatinises. 

Lievrite is found associated with pyroxene in subordinate 
masses in the mica-schist of Elba, also (according to Dana) in 
the granite of Predazzo in Tyrol. 

46. Tourmaline (Schorl). Rhombohedral, eminently hemi- 
morphous. Crystals mostly columnar, imbedded or attached, 
also massive, fibrous, or granular aggregates. Cleavage rhom- 
bohedral, very imperfect. H. = 7 7'5. S.Gr. = 2'94 3'3. 
Colourless, seldom transparent, most usually black, also brown, 
red, blue, green, &c. Lustre vitreous. Every degree of pellu- 
cidity from transparent to opaque. Very eminently polar 
electric. Cp.= very various and complicated. The following 
ingredients take part in its composition : Si, B, P, F, K, Na, 
Li, Ca, Mg, Fe, Mn, Al, Fe, Mn. The oxygen ratio of all the 
bases in this compound (including boracic acid as a base) to 
the silica is constant, and is =4 : 3. Bp. very variable, in part 
fusible (in different degrees), in part intumescent, and in part 
not. All kinds of tourmaline, when mixed with fluor-spar and 
sulphate of potash, exhibit the reaction for boron. Not affected 
by muriatic acid. Sulphuric acid almost completely decomposes 
the powder of fused tourmaline after lengthened digestion. 

Tourmaline is of very frequent occurrence ; but is almost 
exclusively confined to the plutonic-igneous and the meta- 
morphic rocks. It is an essential constituent of schorl rock ; 
accessory in granite, granulite, mica-schist, topaz-rock, and it 
sometimes appears in such quantity in these rocks as to cause 
varieties to be specially named after it. [See post.] It is 
unknown in augitic and volcanic rocks. In dolomite it ap- 
pears exceptionally (Capo Longo, south of St. Gotthard) ; also 



38 MINERALS. 

in sandstone, but only in neighbourhood of intruded plutonic 
rocks. -, K 

The origin of tourmaline is sometimes contemporaneous 
with that of the mother rock, sometimes it is a secondary 
product occasioned by metamorphism (percolation of fresh- 
water springs ?). It has not yet been artificially produced. 

Tourmaline is also known in pseudomorphs after felspar (in 
the granite of Trevalgan, Cornwall), and on the other hand 
pseudomorphs of mica, chlorite, and steatite after tourmaline, 
occur in many places. 

(#) GARNET SECTION. 

The affinity of the different minerals of this section to each 
other consists in their containing the like ratio of oxygen 
between the acids and bases. 

47. Chrysolite (Olivine, Peridot). Trimetric. The crystals 
usually columnar and imbedded (chrysolite), but very often 
massive, in granular aggregates, and disseminated (olivine). 
Cleavage brachydiagonal, tolerably distinct. Fracture con- 
choidal. H. =67. S.G. = 3'3 3-5. Lustre vitreous. Co- 
lour green, asparagus-green, olive-green, also yellow and 
brown. Transparent to translucent. (Chrysolite usually in- 
cludes the transparent crystals of paler colour, while olivine, 
so called from the olive-green tint, is applied to imbedded 
masses and grains of inferior colour and clearness. Dana.) 
Cp. = (Mg,Fe) 3 Si, with some Mn, Ca, Ti, and H. Bp. only 
the varieties containing much iron are fusible. All varieties 
are easily decomposed by sulphuric acid. 

The most beautiful crystals of chrysolite are said to come 
from granitic rocks of Upper Egypt. Fayalite, a variety very 
rich in iron, is found in granite of Mourne Mountains. Other- 
wise this mineral is known as essential ingredient of the rock 
called eulisite. It is an accessory constituent of hypersthene 



GARNET SECTION. 39 

rock (Elfdalen) in talc-schist (Katherinenburg). All these 
occurrences are insignificant compared with the abundance 
and frequency in which both grains and crystals of olivine 
occur in basalts and lavas. In basalt, olivine is almost an 
essential constituent. It is also found in meteoric stones. 

Olivine is, doubtless, usually a purely igneous product. If 
additional proof of this were wanted, it may be found in the 
crystals of an olivine rich in iron which occur in the slags of 
smelting furnaces. 

A rock of New Zealand, which has been called Dunite, 
consists of granular olivine. 

48. Beryl (Emerald, Smaragd). Hexagonal. Crystals co- 
lumnar, either singly attached or imbedded, or clustered in 
geodes ; also fibrous aggregates. Cleavage basal, tolerably 
perfect. Fracture conchoidal to uneven. H. = 7'5 8. 
S.G.=2*68 2'73. Colourless, limpid, but usually green or 
blue. Lustre vitreous. Transparent to translucent at the 
edges only. Cp.=(jrSi' 2 + Ai8i 2 , with some Fe and Cr. Bp. 
fuses with difficulty at the edges to a clouded scoriated glass, 
completely soluble in microcosmic salt. Not affected by 
acids. 

Beryl occurs as an accessory in mica-schist (Salzburg), in 
granite (Mourne Mountains, Bodenmais in Bavaria), in black 
limestone (Muzo in Columbia), and with tin-ore (Saxony). 

PJicnaleite or Phenacite. Cp. GSi. Rhombohedral crys- 
tals, and occurs under precisely similar conditions to beryl. t 

49. Garnet. Monometric, in rhombic dodecahedrons or 
trapezohedrons or in combinations of both. Crystals singly 
attached or imbedded or clustered in geodes, also massive, 
in granular to compact aggregates. Cleavage indistinct, do- 
decahedric. Fracture conchoidal, or uneven and splintery. 
][.=6-5 7'5. S.G.==3'15 4-3. Seldom colourless, usually 
green, yellow, red, brown or black. Lustre vitreous to 



40 MINERALS. 

resinous. Transparent, translucent, opaque. Cp. extremely 
manifold, so that six groups may be distinguished of essen- 
tially different composition, passing over, however, one into 
the other. The common formula may be thus given : B 3 Si-f 
RSi, in which formula E,= (Ca, Fe, Mn, Mg), and R=(A1, 
Fe, Cr). Bp. fuses with considerable ease to a green, brown, 
or black glass, which is frequently magnetic. With phosphor- 
salt gives a siliceous skeleton, otherwise iron and manganese 
reaction. In raw state little affected by muriatic acid, but 
after fusion easily and completely decomposed by that acid, 
with a gelatinous precipitate of silica. 

Almandine, Grossularite, Essonite, Common or Aplome Garnet, 
Colophonite and Melanite are varieties chiefly distinguished by 
their colour and different degrees of transparency. 

Garnet occurs as an essential, and sometimes sole ingredient 
of the following rocks : garnet rock, eklogite, eulisite, kinzi- 
gite. It likewise is a very frequent accessory in granite, 
granulite, vitreous trachyte and perlite (in which it would 
appear to be a contemporaneous formation with the mother- 
rock), and in metamorphic rocks (e.g. chlorite- schist, mica- 
schist), where it is probably a product of the very process of 
metamorphism. In limestone and sandstone rocks (Killan 
and Wexford in Ireland), and in lavas of Vesuvius. 

50. Pyrope. Monoclinic, crystals almost always rounded 
off at the edges, imbedded, or scattered loose in alluvial soil. 
Fracture conchoidal. H.=7'5. S.G.=3'69 3'8. Colour 
deep hyacinth to blood-red. Lustre vitreous. Transparent 
or very translucent. Cp. a magnesian alumina- garnet, with a 
considerable portion of the magnesia replaced by Fe and 
Cr. Bp. becomes black and opaque at a red heat, but re- 
sumes its transparency and red colour on cooling. With 
borax, gives the reaction of chromium. Not affected by 
acids unless previously fused. 



GARNET SECTION. 41 

Pyrope is a very characteristic accessory constituent of 
many kinds of serpentine (Saxony), and of the opal-rock 
termed vitrite (Bohemia). 

51. Zircon {Hyacinth). Dimetric. Crystals columnar or 
pyramidal, singly imbedded or attached. Cleavage pyramidal 
and prismatic, imperfect. Fracture conchoidal to uneven. 
H.=7'5. S.G.=4 47. Colourless, rarely white, usually 
coloured yellow, red or brown. Lustre adamantine, vitreous. 
Every degree of transparency. Cp. = ZrSi, with little Fe. 
Bp. infusible, only soluble with borax. Partially decomposed 
in sulphuric acid after long digestion. Not affected by any 
other acid. 

Zircon occurs in many rocks (more or less abundantly), 
usually as an accessory ingredient only, viz. in zirconsyenite 
(Norway, Ural) ; in granite (Criffel, Kircudbright and New 
Jersey) ; in basaltic lavas of extinct volcanoes (Rhenish 
Prussia) ; and in volcanic tufa (Auvergne) ; in granular lime- 
stone (Hammond). 

52. Idocrase (Vesuvian, Egeran, Wiluit). Dimetric. Crys- 
tals usually columnar or pyramidal, imbedded and attached ; 
also massive in fibrous and compact aggregates. Cleavage 
prismatic, imperfect. Fracture uneven and splintery. H.= 
6'5. S.G. = 3*45. Colour yellow, green or brown. Lustre 
vitreous or resinous. Transparent, translucent, opaque. Cp.= 
R 3 Si + RSi, and R= principally Ca, Fe, Mg, with H up to 
3 per cent. R=A1, Fe. Bp. fuses easily, with effervescence, 
to a yellowish-green or brownish glass. With microcosmic 
salt it produces the reaction of iron and a siliceous skeleton. 
In raw state, imperfectly decomposed by muriatic acid, 
but after fusion, completely decomposed with a gelatinous 
precipitate of silica. 

Idocrase occurs as an accessory in old lavas of Vesuvius ; in 
serpentine (Mussa Alp, Piedmont) ; in dolomite (Fassa Thai, 



42 MINERALS. 

where it is an unmistakable product of metamorphism) ; and 
in metalliferous veins (Swarzenberg, Saxony). 

Its igneous origin, at least in part, is proved by the appear- 
ance of similar products in slags of furnaces. 

53. Scapolite (Wernerite). Dimetric. The crystals columnar, 
attached and imbedded, also clustered in geodes, or massive 
and granular. Cleavage prismatic, tolerably perfect. H.= 
5 5*5. S.Gr.= 2'6 2*7. Colourless, or coloured pale green, 
green, or reddish. Lustre vitreous to resinous. Semi-trans- 
parent to opaque. Cp. very fluctuating, in part answering 
to the formula : B 3 Si 2 + 2AlSi, with Ca, Na, some H and Fe. 

Scapolite is an essential constituent of wernerite rock ; it 
also occurs as an accessory in granite and other crystalline 
rocks, likewise in limestone, but in that case usually near the 
margin of intruded granites. Finally in veins of ore ( Arendal) . 

Heionite and Mellilite. Limpid crystals found in the marble 
blocks of Somma, and Mellilite, dirty yellow, found in nepheline 
rocks at Capo di Bove near Rome, are two minerals very 
closely allied to scapolite. 

54. Epidote (Pistacite, Zoisite). Monoclinic. Crystals co- 
lumnar, extended in the direction of their horizontal axis, 
usually in geodes, also massive and in fibrous, granular, or 
compact aggregates. Cleavage orthodiagonal, very perfect, 
hemidomatic perfect. Fracture conchoidal to uneven. H. = 
6 7. S.G. = 3'2 3*5. Almost always coloured, viz. green, 
yellow or grey. Lustre vitreous, and on the cleavage surfaces 
adamantine. Transparent to opaque. Cp. = R 3 Si-f 2RSi, in 
which formula R Ca, with some Mg and up to 2 per cent H ; 
R=A1, Fe. Bp. variable ; after being subjected to strong 
heat or melted, all varieties may be decomposed by muriatic 
acid and they become gelatinised. 

Zoisite is grey, with Ca and Al ; it occurs as an accessory in 
granular limestone and granite (Fichtelgebirge). 



GARNET SECTION. 43 

Pistacite is green and rich in Fe. It occurs as an accessory 
and very frequently in hornblende rocks, and is probably 
the product of decomposition of hornblende. It also occurs 
in beds of iron-ore (Arendal). 

55. Orthite (Allanite, Cerine). Monoclinic, isomorphous 
with epidote, but seldom occurs in distinct crystals. More 
usually massive, in granular and short fibrous aggregates. 
Fracture conchoidal to uneven. H. 5 5*6. S.G. = 3'3 4'2. 
Colour, pitch-brown to black. Streak greyish or greenish. 
Lustre imperfect, metallic to vitreous and resinous. Trans- 
lucent at the edges to opaque. Cp. variable. In part, R :} Si + 
JiSi, in which R= Al and R=Ce, Ca, Mg, with little La and H, 
and in the variety orthite, Y. Bp. on charcoal, puffs up slightly 
and fuses to a black glass ; with borax fuses easily and makes 
with oxidising flame a bead of blood-red colour in the heat and 
yellow on cooling ; with the reduction flame the bead is green. 

Orthite occurs as an accessory in granite, especially in cer- 
tain narrow dykes of granite, rich in felspar, which traverse 
hornblendic rocks (Greenland, Dresden) ; in zirconsyenite 
(Hitteroe in Norway), where the crystals are a foot in height ; 
sometimes in porphyries (Totun Fjeld in Norway). 

56. Gadolinite. Monoclinic, but seldom in crystals, usually 
massive and imbedded. Fracture conchoidal to uneven. H.== 
6-57. S.G. = 4 4-3. Pitch- and raven-black. Streak 
greenish-grey. Lustre vitreous, resinous. Translucent at 
the edges to opaque. Cp. various, in general R 3 Si ; and R= 
Y, Ce, Fe, Ca. Bp. puffs up slightly without fusing, glows 
vividly and burns to a light-grey colour. Gelatinises with 
muriatic acid. 

Gadolinite occurs chiefly in granite, and as an accessory, 
imbedded (Fahlun in Sweden, Hitteroe in Norway). 

57. Axinite (Thumite). Triclinic. Crystals singly at- 
tached, or clustered in geodes, also massive, in scaly aggre- 



44 MINERALS. 

gates. Cleavage indistinct. H. = 6'5 7. S.G.=3'3. Colour 
clove-brown, grey, or plum-blue. Transparent to translucent 
at edges only. Exhibits trichroism in an eminent degree. 
Cp. very complicated = B, 3 Si + 2RSi + JB Si; and R = Ca, 
Mg, K ; R = Fe, Mn. Bp. melts easily, and with intumescence, 
to a dark green glass, which becomes black in the oxidation 
flame ; with fluor-spar and sulphate of potash gives the reaction 
of boracic acid. After fusion it gelatinises completely with 
muriatic acid. Axinite occurs in the geodes of granite (Oisans, 
St. Gotthard), or in metalliferous veins (Botallack in Cornwall ; 
Kongsberg in Norway). 

58. Cordierite (Dickroite, Peliom, lolite). Trimetric. Crys- 
tals usually columnar, hexagonal, also massive and dissemi- 
nated. Cleavage brachydiagonal, tolerably perfect. Fracture 
conchoidal to uneven. H. = 7 7*5. S.G. 2*6. Colourless, but 
usually coloured bluish-grey, violet-blue, or brownish. Lustre 
vitreous ; in fracture eminently resinous. Transparent to 
translucent, beautiful trichroism. Cp. R 3 Si 2 -f 3AlSi ; and 
R=Mg, Fe, Mn and H. Bp. fuses with difficulty at the edges 
to a glass ; dissolved with difficulty in borax. Little affected 
by acids. 

Cordierite occurs as a substitute for quartz, and an essential 
ingredient in several granites and in metamorphic gneiss, under 
circumstances pointing to an igneous origin, or to an origin 
from contact with igneous masses (Saxony). It also occurs 
in beautiful crystals in metalliferous veins (Bodenmais in 
Bavaria). 

FaMunite and Finite are products of transmutation from 
cordierite, or (according to some authors) from nepheline. 
They occur porphyritically in granite. 

Liebnerite and Oosite are like products. They occur chiefly 
in porphyry rocks. 



TANTALATES, TITANATES, VANADATES. 45 

C. TANTALATES (OR COLUMBATES) TITANATES, 
VANADATES. 

The minerals here grouped occur very frequently as acces- 
sory ingredients in plutonic and igneous rocks, and are for the 
iinost part of contemporaneous origin with the rocks in which 
they occur. 

59. Pyrochl&re. Monometric, usually in octahedrons (cry- 
stals or grains imbedded.) Fracture conchoidal, brittle. H.= 
55-5. S.G.=3'8 4-3. Colour dark reddish- and. blacjdsh- 
brown. Streak light brown. Lustre vitreous. Translucent 
at the edges to opaque. Cp. = (Ca,Fe,Ce,Mn)(Cb,fi) with 
some NaF and H. Bp. becomes yellow and fuses with diffi- 
culty to a brown slag, previously (sometimes) emitting an 
intense light. When powdered, it is decomposed in concen- 
trated sulphuric acid. 

Pyrochlore occurs as an accessory in granite and syenite 
(imbedded), (Miask, Brevig in Norway), also in granular 
limestone (Kaiserstuhl in Baden). 

60. Perofskite. Monometric, usually in cubes or octahedrons. 
Crystals attached or imbedded, also massive. Cleavage cubal. 
H. =5'5. S.G.=4. Colour greyish- to iron-black, or reddish- 
brown. Streak greyish-white. Lustre metallic-adamantine. 
Opaque. Cp.^CaTi, with small quantity of Fe. Bp. in- 
fusible. Scarcely affected by acids. 

Perofskite occurs as an accessory in chlorite schist (Slatoust, 
in the Ural) in talc schist (Zermatt), and in granular limestone 
(Kaiserstuhl). 

61. Tantalite. Trimetric. Crystals usually columnar, also 
massive and disseminated. Fracture conchoidal to uneven. 
H.=6 6-5. S.G.=7'1 7'9. Colour iron-black. Streak 
brown. Lustre adamantine metallic. Opaque. Cp. = 
(Fe,Mn)(Ta,Cb 2 ), w ith sometimes some Ca and up to 16 per 



46 MINERALS. 

cent, of Sn. Bp. unchanged. Not affected, or very little 
affected, by acids. 

Tantalite occurs as an accessory in granite, imbedded, and is 
usually associated with beryl and tourmaline (Finland, Sweden). 

62. Columbite (Nwbite). Trimetric, usually in thick tabular 
or broad columnar crystals. Cleavage macrodiagonal, very 
distinct, brachydiagonal distinct. Fracture conchoidal to un- 
even. H.=6. S.G. = 5'4. 6'4. Colour brownish-black to 
iron-black. Streak reddish-brown to black. Lustre metallic 
adamantine. Opaque. Cp. = (Fe,Mn) 3 Cb 2 , with little Ca and 
Sn. Bp. infusible, unchanged. Not affected by acids. 

Columbite occurs as an accessory in granite, associated with 
beryl and tourmaline (Bodenmais in Bavaria, Connecticut and 
Massachusetts), also imbedded in cryolite (Greenland). 

63. Wolilerite. Trimetric. Distinct crystals very rare, 
usually massive and disseminated. Fracture conchoidal. H. = 
5'5. S.G. - 3*4, Colour wine-yellow to honey-yellow, or 
yellowish-brown. Lustre resinous in the fracture. Trans- 
lucent. Cp.=a silicate of Ca, Na, Ta, Zr. Bp. at first un- 
changed, after some time fuses to a yellow glass. Decomposes 

in concentrated muriatic acid. 

v 

Wohlerite occurs as an accessory in zirconsyenite (Brevig 
in Norway), in syenite and miascite (Ditro in Transylvania). 

64. Titanite (Sphene, Menochine ore). Monoclinic, frequently 
crystallised, prisms and tabular, imbedded and attached, twins 
frequent, also massive and in scaly aggregates. Cleavage 
indistinct. H. = 5 5'5. S.G.=3'4 3'56. Colour grey or 
brown. Lustre adamantine, often resinous. Semi-transparent 
to opaque. Cp.=2CaSi=CaTi :{ . Bp. fusible only at the edges. 
With microcosmic salt and metallic tin gives the reaction of 
titanium in the reduction flame. Incompletely decomposed 
by muriatic acid ; completely decomposed by sulphuric acid, 
gypsum being formed. 



SULPHATES. 47 

Ghreenovite is red-coloured titanite containing Mn. 

Titanite occurs as an accessory in the mica-schist of the 
Alps, and there usually in cruciform twin crystals, in gneiss 
(Massachusetts), in granite (Greenland), in syenite and zir- 
consyenite (Strontian, Argyleshire ; Arendal), in volcanic 
rocks, rich in felspar (Laachersee, Andernach on the Rhine), 
in phonolite (Bohemian Mittelgebirge), in beds of iron-ore 
(with pyroxene in Arendal), finally in granular limestone (in 
many localities in North America). 

65. Volborthite. Hexagonal. Crystals are small, often only 
scaly particles on an earthy incrustation. H.=3 3'5. S.G.= 
3'45 3'86. Colour olive- or grass-green, also yellow. Streak 
almost yellow. Lustre mother-of-pearl, vitreous. Translucent 
in thin plates. Cp. = (Cu,Ca) 4 V + H. When heated in glass 
tube gives out water. Bp. fuses easily on charcoal, and at a 
higher temperature consolidates to a slag, resembling graphite, 
which slag contains grains of metallic copper. It is soluble 
in muriatic acid. 

Volborthite occurs as an accessory ingredient in many sand- 
stones of the Permian formation of Russia, or as incrustation 
on the walls of clefts in the same rocks. 

D. SULPHATES. 

(a) ANHYDROUS SULPHATES. 

66. Barytes (Heavy Spar). Trimetric. Crystals tabular or 
columnar, very various; also lamellar, fibrous, granular, or 
compact. Cleavage perfect in the planes of the brachy- and 
macro-diagonals. H.=2'5 3'5. S.G.-4'3 47. Colour- 
less, limpid, or variously coloured, white, yellow, brown, or 
red. Lustre vitreous or resinous. Transparent, translucent, 
opaque. Cp.=BaS, with admixture, in small quantities, of 
other bases, such as Ca, Sr, and Fe. Bp. decrepitates, and fuses 



48 MINERALS. 

with difficulty. Colours the flame yellowish-green. Not 
affected by acids. 

Barytes seldom occurs as an independent rock. It occurs 
as an accessory in the form of lamellar nodules in the clay 
strata of Monte Paterno near Bologna, where it is called 
Bologna-spar or Bolognese stone. It also occurs in the 
cavities of fossils in the Swabian Jurassic formation ; also very 
frequent in veins of ore. 

67. Celestine. Trimetric, isomorphous with barytes, also 
the same cleavage, frequently fibrous, granular, or compact. 
H. 3 3-5. S.Gr. = 3'9. Colourless, limpid, but usually 
white, rarely blue. Lustre vitreous to resinous. Transparent, 
translucent. Cp.=SrS. Bp. decrepitates and fuses without 
difficulty to a milk-white bead. If moistened with muriatic 
acid, it colours the flame carmine-red. It is only slightly 
affected by acids. 

Celestine only occurs as an accessory constituent in rocks. 
Sometimes it is found in layers of a fibrous texture imbedded 
in marly limestone (Jena), in lamellar or radiated nodules in 
dolomite (Seisser Alps), or in fossils (Swabia), also in many 
metalliferous veins. 

68. Anhydrite (Muriacite, Karstenite) . Trimetric. Crystals 
thick, tabular, but rare ; usually massive, in granular or com- 
pact aggregates. Cleavage macro- and brachy- diagonal, very 
perfect, basal perfect. H. = 3 3'5. S.G. = 2'8 3. Colour- 
less, white, but most frequently light bluish-grey or reddish- 
grey. Lustre vitreous, on the faces of basal cleavage, resinous. 
Cp. = CaS. Bp. fuses with difficulty to a white enamel ; with 
borax effervesces, and fuses to a transparent glass, which on 
cooling becomes yellowish. Little soluble in acids. 

Anhydrite occurs as an independent rock, associated with 
gypsum and rock-salt (frequent in the Alps). It also occurs 
in metalliferous veins (Andreasberg). 



SULPHATES. 49 

69. Glauberite. Monoclinic, also massive, in thin lamellar 
aggregates. Cleavage basal perfect. H.=2*5 3. S.G.= 
2*6 2 - 8. Colourless and coloured, greenish, yellowish or 
reddish-white. Lustre vitreous to resinous. Translucent. 
Taste salt and bitter. Cp. = NaS + CaS. Bp. decrepitates 
violently, and fuses readily to a transparent glass. Colours 
the flame reddish-yellow. 

Glauberite occurs as an accessory in rock-salt (Villa Rubia 
in Spain, Berchtesgaden in Bavaria, Tarapaca in Peru). 

(>) HYDROUS SULPHATES. 

70. Gypsum (Alabaster, Selenite). Monoclinic. Crystals 
prismatic and tabular, various, frequently twins, also massive, 
fibrous, lamellar, granular, or compact. Cleavage clinodiagonal, 
very perfect, hemipyramidal less perfect. Sectile. In thin plates 
flexible. H. = 1'5 2. S.G.=2'3. Colourless, limpid, or 
white, sometimes variously coloured grey, flesh-red, yellow, 
&c. Lustre mother-of-pearl on the faces of most perfect cleav- 
age, silky on the hemi- pyramidal faces, otherwise vitreous. 
Transparent, translucent, opaque. Cp. = CaS=2H. In matrass 
yields much water. Bp. becomes dull and white, exfoliates 
and fuses with difficulty to a white enamel, which has an 
alkaline reaction. Soluble in 460 parts of water, in acids 
somewhat more easily. 

Gypsum occurs as an independent rock in sedimentary for- 
mations, or in metamorphic schists (mica-schist of the Alps). 
It occurs accessorily in the form of crystals or nodules in 
clay-marls, rarely in metalliferous veins or dykes ; sometimes, 
however, in mines as a recent product. 

The origin of gypsum may be either by wet or dry process, 
or by metamorphism. It is formed (1) in volcanic districts by 
fumes of sulphuric acid and sulphuretted hydrogen issuing 

from cracks or other openings in the ground, and act:'ng upon 

E 



50 MINERALS. 

lavas previously containing pyroxene and labradorite ; (2) by 
wet process, where pyrites is decomposed in the neighbour- 
hood of lime, or as a sediment from the evaporation of sea- 
water. The latter process may be observed taking place arti- 
ficially in salt pans ; (3) by metamorphism from anhydrite by 
simple absorption of water. 

71. Alunogen (Hair Salt). Occurs in capillary or acicular 
crystals or crystalline masses of irregular form, usually in 
crystalline crusts or reniform aggregates of fibrous structure. 
H.=1'5 2. S.G.=l-6 1-8. Colour white and yellowish, 
or greenish. Lustre silky. Cp. = AlS 3 + 18H. Easily soluble 
in water. If heated in test tube, it intumesces and gives out 
water. 

Alunogen is sometimes the product of volcanic action (vol- 
cano of Pasto, Milo Isle), sometimes a result of the decom- 
position of pyrites in coal districts, and in alum-shales (Bonn, 
Dresden) ; sometimes is found as an efflorescence in numerous 
places in the United States. 

72. Native Alum. Chemically speaking there are several 
subspecies. Crystallographically all monometric, and usually 
in octahedrons ; also occurs in fibrous masses. Fracture con- 
ohoidal. H.=2 2-5. S.G. = 1 -61-9. Soluble in water. 
Taste sweet-astringent. Cp.=RS + AlS 3 -i-24H. According 
to the various bases, different species are distinguished, viz. : 
Potash-alum, soda-alum, magnesia-alum, iron-alum, manganese- 
alum, and ammonia-alum. Bp. on charcoal, efflorescence ; 
with cobalt solution blue. 

Alum is found in the vicinity of the crater of ^tna, filling 
clefts in the Coal and Browncoal formations, especially in 
pyritous shales (Saarbrucken, Bohemia), and as an efflorescence 
on other minerals or rocks. In fresh alum-slate no alum is 
contained, but the latter is only developed in that rock by 
weathering and the consequent decomposition of the pyrites 
contained in it. 



SULPHATES. 51 

73. 'Epsomite (Epsom Sa.lt). Trimetric. Crystals columnar, 
usually in granular, fibrous, or earthy aggregates. Cleavage 
brachydiagonal. H.=-2'25. S.G.=175. Colourless. Trans- 
parent. Taste saline bitter. Cp.=2MgS + 7H. Easily soluble 
in water. Bp. if heated in test tube gives water, fuses, and 
then remains unchanged. On charcoal it effervesces violently, 
and shows alkaline reaction ; if heated with cobalt solution, 
becomes rose-pink. 

Epsomite occurs as an efflorescence from marshy ground 
(Steppes of Siberia), and from many kinds of rock (gneiss 
near Freiberg, alum-slate at Idria), also in solution in spring 
waters (Epsom, Saidschutz in Bohemia). 

74. Glaubersalt (Mirabilite). Monoclinic, usually incrusted. 
H.=1'5 2. S.G. = 1-48. Colourless, transparent. Taste 
cooling, and saline bitter. Cp.=NaS + 10H. Easily soluble 
in water, quickly decomposing, and falling to powder in the 
atmosphere. Bp. in test tube it melts in its water of crystal- 
lisation. It colours the flame reddish-yellow. 

Glaubersalt occurs as an independent rock (Guipuscoa in 
Spain), accessory in rock-salt strata (Berchtesgaden) ; also in 
mineral springs (Carlsbad in Bohemia), and salt lakes. 

75. Alunite (Ahimstone) . Bhombohedral. The crystals 
mostly very small, and clustered in geodes. Usually massive, 
in granular, earthy, and compact aggregates. It occurs mixed 
and interlaced with quartz, hornstein, and felsite. Cleavage 
basal. H. = 3-5 4. S.G. = 2'6 27. Colourless, white, yel- 
low, or reddish. Lustre vitreous, with mother-of-pearl lustre 
on the basal cleavage faces. Translucent. Cp. = KS-f 3A1S-J- 
6H. In test tube gives out water. Bp. decrepitates violently 
and is infusible. Not affected by muriatic acid ; soluble in 
heated concentrated sulphuric acid. Alum is manufactured 
from this mineral by heating and adding water to it. 

Alunite is met with in the largest known quantities at La 

2 



52 MINERALS. 

Tolfa near Rome, where it occurs in small geodes in decom- 
posed trachytic rocks, and owes its origin to the action of 
sulphuric acid (a product of volcanic agency) upon the rock 
during long periods of time (Muzay, Hungary ; Montdore, 
Auvergne). 

E. BOKATES. 

76. Boracite. Monometric, tetrahedral. The crystals some- 
times show combinations of the cube, the rhombic dodeca- 
hedron, and tetrahedron. Always porphyritically imbedded. 
Cleavage imperfect. Fracture conchoidal. Brittle. H. = 7. 
S.Gr. = 2'97. Colourless, white or greyish, yellowish, greenish. 
Lustre vitreous to adamantine. Transparent to translucent at 
edges only. Cp.=Mg 3 B 4 . Bp. intumesces, fuses with diffi- 
culty, forming a pearl which, whilst hot, is transparent and 
yellowish, and when cooled is white and crystalline, acicular. 
It colours the flame green when fused with sulphate of soda 
and fluor spar. In muriatic acid it is perfectly soluble. 

Boracite occurs, as an accessory only, in gypsum, anhydrite, 
or rock-salt (Liineburg in Hanover, Seegeberg in Holstein, 
Luneville in France ; in the last place in radiated fibrous 
masses). A fine-grained to compact rock, which occurs in 
subordinate masses in the salt mountains of Stassfurt near 
Magdeburg, consists essentially of boracite with some chloride 
of magnesium. It is called stassfurtite. 

77. Borax (TinkaT). Monoclinic, isomorphous with pyrox- 
ene. The crystals usually broad and short, columnar. Cleavage 
clinodiagonal and prismatic. Fracture conchoidal. H. = 
2 2'5. S.G.=:1'72. Colourless, or more usually yellowish 
and greyish- white. Lustre resinous. Translucent. Cp.= 
NaB 2 -f 10H ; usually impure. Bp. decrepitates with rapid 
heating, pufis up violently, becomes black, and finally melts to 
a transparent colourless powder. It tinges the flame reddish- 



PHOSPHATES. 53 

yellow. If moistened Avith sulphuric acid, it tinges the flame 
green. 

Borax is met with in loose crystals and crystalline grains 
or incrustations, associated with rock-salt, on the shores of 
several lakes in Thibet, where it is a recent formation. Clear 
lake in California, in crystals several inches long. 

F. PHOSPHATES. 

(a) ANHYDROUS PHOSPHATES. 

78. Apatite (Spargelstein, Phosphorite). Hemihedral hexa- 
gonal. The crystals short, columnar, or tabular ; also massive, 
in granular, fibrous, or compact masses (phosphorite). Cleav- 
age prismatic and basic. Fracture conchoidal to uneven, and 
splintery. Brittle. H.=5. S.G.=3'25. Colourless, white, 
but more usually light green, blue, or grey. Lustre vitreous 
on crystal faces ; resinous on fracture or cleavage surfaces. 
Cp.=3Ca 3 P + Ca(Cl,F), with sometimes Mg and Fe. Bp. 
only fusible in thin laminae. If moistened with sulphuric acid, 
colours the flame bluish-green. Soluble in muriatic and in 
nitric acids. 

Apatite is met with (1) as an independent rock or in con- 
cretions, principally in strata of the Browncoal formation, more 
rarely in the Chalk formations, always massive (phosphorite) ; 
frequent in the Oberpfalz of Bavaria : (2) as an accessory con- 
stituent of rocks, especially the volcanic (nepheline-dolerite 
at Lobau in Saxony ; basalt in Bohemia ; volcanic rocks of 
Tumilla and in meteorites) ; in talc-schist (Zillerthal), and in 
limestone (Gouverneur in North America, Arendal, Pargas) ; 
(3) very frequent in veins of tin-ore. 

It will be therefore seen that apatite in many cases must be 
a formation by wet process, and in others a plutonic product. 
Daubree has succeeded in producing artificial crystals of 



54 MINERALS. 

apatite by conducting fumes of chloride of phosphorus over 
heated quicklime. 

79. Turquois (Calaite). Amorphous in cavities and veins, 
reniform or stalactitic. Fracture conchoidal to uneven. H. = 6. 
S.Gr. 3=2*6 2*8. Colour sky-blue to verdigris-green. Streak 
greenish- white, Lustre feeble. Translucent at the edges to 
opaque. Cp. = Al 2 P + <5H, with some Cu up to 3 per cent. 
If heated in test tube, it gives water, decrepitates violently, 
and becomes black. Bp. infusible ; tinges the flame green. 
Soluble in acids. 

Turquois is met with as an incrustation in the fissures of 
Lydian stone ; very precious varieties in Persia. Also occurs 
in sandstone in Arabia. 

(6) HYDROUS PHOSPHATES. 

80. Vivianite (Blue Iron-Earth). Monoclinic. The crystals 
usually single, attached, also fibrous, divergent, earthy. Cleav- 
age clinodiagonal, very perfect ; in thin laminae, flexible. H. = 
1*5 2. S.Gr. 2*66. Colour indigo-blue to blackish- green, 
sometimes white, and becoming blue by exposure. Lustre on 
cleavage surfaces, mother-of-pearl. Translucent. Cp.=Fe 3 P + 
8H. Bp. in matrass gives out much water, pufis up, and 
becomes particoloured grey and red ; on charcoal burns and 
becomes red, and then fuses to grey, lustrous, and magnetic 
globule. Readily soluble in muriatic and nitric acids. 

Vivianite is usually a product of decomposition from magnetic 
pyrites, in veins traversing the clay slate (St. Agnes, Corn- 
wall), or in granite (Bodenmais in Bavaria). The earthy 
variety is very frequent as an accessory constituent of turf 
mosses and Tertiary clays. Pseudomorphous in form of oysters 
and belemnites in New Jersey, U. S. 

81. Wavellite (Lasionite). Trimetric. The crystals usually 
small, acicular, and clustered to reniform aggregates of radiated 



NITRATES. 55 

structure. H.=3'25 4. S.G.=2'34. Colourless, white, or 
coloured greyish, or a beautiful green or blue. Lustre vitreous. 
Cp. = (Al 4 P + 18H)+JAlF. Bp. in matrass gives cutwater 
and traces of hydrofluoric acid. In the forceps puffs up and 
tinges the flame bluish- green, especially if moistened with 
sulphuric acid. 

Wavellite is met with as an accessory and a secondary 
product in fissures of a soft clay-slate at Barnstaple in Devon- 
shire ; in Lydian stone at Langenstriegis, near Freiberg ; and 
in Devonian sandstone at Zbirow in Bohemia. 

G. NITRATES. 

82. Nitre (Saltpetre). Trimetric. The crystals prismatic, 
isomorphous with aragonite, but usually only very thin, 
capillary, and acicular. Fracture conchoidal. H.=2. S.G. 
= 1'9. Colourless, white and grey. Lustre vitreous. Taste 
saline, cooling. Cp. = KN. Readily soluble in water; defla- 
grates vividly on glowing charcoal. Bp. fuses easily on pla- 
tinum wire, tinging the flame violet. 

Nitre occurs as a separate formation in the caverns of 
several limestone mountains (Ceylon, Calabria), as an efflores- 
cence from the surface of the ground, especially in hot weather 
after rain (Aragon, Hungary, East India) ; also in springs. 

83. Nitratine (Chili saltpetre). Rhombohedric. In crystals, 
and crystalline grains ; cleavage, rhombohedric. H. = 1*5 2. 
S.G.=-2'1 2'3. Colourless or light coloured. Transparent to 
translucent. Taste saline, cooling. Cp. = NaN. Soluble in 
water ; deflagrates in glowing charcoal, but less vividly than 
saltpetre. Bp. fuses, tinging the flame yellow. 

Nitratine is a marine product, found in grains mixed with 
the sand, and associated with gypsum, rock-salt, and glauber- 
salt, occurring at many parts of the coast of Chili. 



56 MINERALS, 

H. CARBONATES. 

(a) ANHYDROUS CARBONATES. 

The most important of the carbonates are those comprised 
in the Calcite group. The calcspar and dolomites form whole 
mountain ranges (limestone and dolomite) as well as isolated 
mineral formations of minor extent in cliffs, fissures, and 
veins. 

They are chiefly of neptunian origin, partly crystalline or 
compact precipitates ; partly formed by springs ; and partly 
the result of organic processes (chalk, coral). There are 
probably no limestone rocks of plutonic origin, although 
carbonate of lime under high pressure is capable of fusion 
without chemical decomposition. The minor mineral forma- 
tions in clefts, veins, dykes, and geodes are doubtless, for the 
most part, the result of infiltration. 

All calcites are rhombohedral in crystallisation. Calcspar 
alone presents great variety of form. Its crystals are grouped 
and interlaced in almost every conceivable shape and fashion, 
and the uncrystallised varieties are fibrous, granular, compact. 
The cleavage of the crystals is rhombohedral, very perfect. 
The angle of the cleavage rhombohedron is the most charac- 
teristic distinguishing feature of the different species, which 
can only be determined in many cases by an accurate measure- 
ment of that angle. Fracture conchoidal, but in the crystal- 
lised varieties it is somewhat difficult to obtain a genuine 
fracture. The colour is usually white, grey, yellowish, reddish, 
or brownish. Lustre vitreous, sometimes resinous. Calcspar 
and magnesite alone are sometimes perfectly transparent, 
the other calcites at most only attain translucence. The Cp. 
of all calcites comes under the general formulae E/C. 

The following are the principal species of this important 
group of minerals : 



CARBONATES. 57 

84. Calcspar {Calcareous Spar, Calcite). H.=2'5 3*5. 
S.G. = 2'5 2-8. Cp. = CaC, usually with small quantities of' 
Fe, Mg, Mn. Bp. infusible, but burns to quicklime with a 
bright light. Readily soluble in muriatic acid, even in large 
pieces, with effervescence, caused by the evolution of carbonic 
acid. 

Limestone, marble, chalk, oolite, pisolite, coral, are some of 
the most important of the very numerous varieties which 
form independent rocks, and will be described hereafter as 
such. Marl is a mixture of clay and lime. Iceland spar is 
a pure transparent variety of calcspar. Anthraconite is 
coloured black by admixture of carbon. It would lead us too 
far to attempt to enumerate all the varieties of this very 
abundant mineral. 

Calcspar stands next to quartz in importance, as consti- 
tuting the mineral of the greatest frequency after it, and 
forming nearly as large a portion of the earth's crust. 

85. Magnesite (Talc-spar). H.=3'5 4*5. S.G.=2'8 3. 
Cp. = MgC, usually also some Fe. Bp. becomes red if heated 
with cobalt solution. Soluble in acids, if powdered and heat 
applied. 

86. Dolomite (Bitter Spar, Brown Spar, Ankerite). H.= 
3-5-^. S.G. =2-85 2-92. Cp.=CaC + MgC, usually with 
admixtures of Fe and Mn. Ankerite is particularly rich in 
iron. Bp. infusible, burns to caustic. Does not usually effer- 
vesce with muriatic acid, and is only soluble in that acid if 
powdered and heat applied. 

87. Breunnerite (Bitter and Brown Spar, in part ; Mesitine 
Spar). Cp.=FeC + 2MgC. H.=4'5. S.G.=3 3'63. 

88. Spathic Iron (Sparry Iron-ore, Siderite). H. = 3'5 4'5. 
S.G. 3'7 3'9. Colour always yellowish-grey or yellowish- 
brown. Cp. FeC, with some Mn, Mg, and Ca. In matrass 
decrepitates and gives out carbonic acid. Bp. infusible ; but 



58 MINERALS. 

becomes black and magnetic. Soluble in acids without heat 
applied (effervescing). 

In the compact state, or when occurring in reniform masses 
or concretions, this mineral is termed SpJicerosiderite, and if, 
moreover, combined with play, Clay Ironstone. 

89. Zinc Spar (Calamine, Galmey, in part). H. =5. S.G. 
=4 4'3. Cp.=ZnC, with small quantities of Fe, Mn, Ca, 
Mg. Bp. loses its carbonic acid, and then shows reaction of 
oxide of zinc. Readily soluble in acids, with effervescence. 

90. Aragonite. Trimetric. Crystals usually columnar, with 
inclination to twin formations. Singly imbedded or clustered 
in geodes ; also occurring in divergent and fibrous aggregates 
and stalk-like, coralloidal shapes (flos ferri), or in the form of 
peastone (pisolite). Cleavage brachydiagonal, distinct ; pris- 
matic, and brachydomatic, imperfect. Fracture, conchoidal 
to uneven. H. =3'5 4. S.G.=2'93. Colourless and coloured 
yellow, wine-yellow, reddish. Lustre vitreous. Transparent 
to translucent. Cp.=CaC, very often with SrC (up to 2 '4 
per cent.), also some CaF. Bp. in matrass decrepitates 
violently, and falls to a white coarse powder ; on charcoal 
burns to caustic lime ; if containing strontian colours the 
flame carmine. Soluble both in muriatic and nitric acids, 
with effervescence. 

Aragonite occurs as an accessory in clay and gypsum 
(Molina and Valencia in Aragon). In clefts and veins of 
vesicular cavities of basaltic rocks (Bilin, Bohemia). Flos- 
ferri is formed in great perfection in the Styrian iron mines. 
A fine fibrous variety called satinspar is found in thin silklike 
veins traversing the shale at Alston Moor. Peastone (sprudel- 
or erbsenstein) occurs in great beauty at Carlsbad. 

Aragonite is entirely a watery product. It is said that 
whereas cold springs can only produce calcspar, hot springs give 
birth to aragonite. Moreover, according to Becquerel, aragonite 



. CARBOXATES. 59 

is formed by the action of a saturated solution of NaC 2 on 
gypsum, but calcspar if the solution of NaC 2 be much diluted. 

(6) HYDROUS CARBONATES. 

91. Trona (Urao). Monoclinic. Crystals broad, columnar ; 
in direction of horizontal axis, also in fibrous and divergent 
aggregates. Cleavage orthodiagonal, perfect. H. =2 '5 3. S.G. 
=2*1. Colourless or grey. Lustre bright vitreous. Transparent. 
Cp. = Na 2 C 3 + 4H. Sometimes with some NaCl. Does not alter 
by exposure in a dry atmosphere. Yields water in matrass. 
Soluble in dilute muriatic acid with brisk effervescence. 

Trona forms an independent rock (Figzan, North Africa). 
It forms a crust on the ground on mountain slopes at Mara- 
caibo in Peru ; and occurs as an efflorescence near Sweetwater 
River, Rocky Mountains, mixed with sulphate of soda and 
common salt. 

92. Natron {Carbonate of Soda). Monoclinic. Is only 
known in nature in form of incrustation, or mealy efflorescence 
on the surface of the ground, or various rocks. H. = 1 1'5. 
S.Gr. 1'4. Colourless, white or grey. Lustre vitreous, dull. 
Taste alkaline. Cp. NaC-f 10H. Unlike trona it weathers 
rapidly on exposure to the air. Liquifies at a moderate tem- 
perature, and dissolves in its own water of crystallisation ; 
otherwise, however, has the same attributes as trona (Egypt, 
Hungary, Vesuvius). 

93. Malachite. Monoclinic. In aggregates composed of 
minute crystallisations, acicular and capillary, lamellar, botry- 
oidal, and stalactitic, fibrous to compact. Cleavage when crys- 
tallised basal and clinodiagonal, very perfect. H. = 3'5 4. 
S.G 3*7 4. Colour emerald- to verdigris-green. Streak 
verdigris- to apple-green. Lustre of crystals adamantine and 
vitreous ; of aggregates silky to dull. Translucent to opaque. 
Cp. = Cu 2 C + H. In matrass yields water and blackens. Bp. 



60 MINERALS. - 

fuses on charcoal, and is finally reduced to copper. Soluble 
in acids, with effervescence. 

Malachite occurs as an accessory in various rocks. It is 
doubtless usually, if not always, a product of the decomposition 
of copper-ores (Siberia; Chessy near Lyons; Cornwall). It 
very frequently is found in the form of a pseudomorph of 
azurite and red copper-ore. 

94. Azurite (Lasurite, Blue Copper-ore). Monoclinic. Crys- 
tals columnar or tabular, usually in clusters or geodes ; also 
massive and earthy varieties. Cleavage clinodomatic, toler- 
ably perfect. Fracture conchoidal to uneven, and splintery. 
H.^3'5 4-25. S.G-.=3'5 3-8. Colour azure-blue, in earthy 
varieties smalt-blue. Lustre vitreous. Translucent, opaque. 
Cp. Cu 3 C 2 + H. Bp. similar to malachite. 

Azurite resembles malachite in the places where it is found 
in nature, and in the mode of its occurrence in other respects. 
The earthy variety of azurite may, from its outward appearance, 
be easily mistaken for vivianite. 

V. 

I. OXIDES OF ELEMENTS OF THE HYDROGEN GKOUP. 

The oxides collected under this head properly speaking 
belong more justly to the family of earths (Nbs. 1 3). We 
have, however, postponed their consideration in order to give 
place as far as possible to those minerals which are more im- 
portant to the geologist. 

(a) ANHYDROUS OXIDES. 

95. Spinel (Ceylonite, Pleonaste, Automolite, Gahnite). 
Monometric, usually octahedrons and rhombic dodecahedrons. 
Crystals singly imbedded and attached, seldom gathered into 
geodic clusters. Cleavage octahedral. Fracture conchoidal. 
H. = 8. S.Gr. 3-5 4-9. Usually coloured, red-blue, green, 
yellow, brown, or black. Lustre vitreous, sometimes 



ANHYDROUS OXIDES. 61 

resinous. Transparent, translucent, opaque. Cp.=RAl; R = 
(Mg,Fe,Ca,Zn,Mn), and a part of the Al is sometimes replaced 
by Fe and a little Cr. The varying composition gives rise to 
distinguishable varieties of the mineral. Thus MgAl, red, 
transparent, is spinel proper ; (Mg,Fe)Al, black, translucent 
at the edges, is pleonaste ; ZnAl, greenish-black, translucent at 
the edges, automolite. Bp. the red varieties infusible, but lose 
their colour ; on cooling the colour returns. The black 
varieties fuse to a dark-green bead. The zinc-spinels with 
soda give oxide of zinc. Not affected by acids. 

Spinel occurs as an accessory in granular limestone (pleon- 
aste at Monzoni ; blue spinel in North America in several 
places), in gneiss and talc-schist (the automolite of Fahlun) ; in 
the vesicular cavities of volcanic rocks (Somma), and in allu- 
vium (Ceylon). Sometimes spinel is a product of metamor- 
phosis, e.g. of the action of syenite on limestone, at Monzoni. 
Ebelmen has also succeeded in producing spinel artificially 
by igneous means. 

96. Magnetic Iron-ore (Magnetite, Oxydulated Iron). Mono- 
metric, most usually in octahedrons and rhombic dodeca- 
hedrons. Crystals imbedded and attached, and clustered in 
geodes ; very generally massive in granular or compact aggre- 
gates, also earthy (eisenmulm). Cleavage octahedral. Frac- 
ture conchoidal to uneven. Brittle. H.=r5'5 6*5. S.G.= 
4*9 5 '2. Colour iron-black. Streak black. Lustre metallic. 
Opaque. Yery strongly magnetic. Cp.=FeFe, sometimes with 
some Mg. Bp. fuses with difficulty, and with borax gives iron 
reaction. The powder completely soluble in muriatic acid. 

Magnetic iron-ore is found in separate beds (Arendal, 
Dannemora) ; it also occurs as an accessory in many rocks, 
especially in chlorite-chist, talc-schist, serpentine, granite, 
syenite, basalt, and limestone. 



62 MINERALS. 

97. Chromic Iron-ore (Chromite). Monometric in octa- 
hedrons, usually massive, in granular aggregates, and dis- 
persed. Cleavage octahedral, imperfect. Fracture conchoidal 
to uneven. H.=5'5. S.G. =4'3. Colour brownish-black. 
Streak brown. Lustre semi-metallic. Opaque. Sometimes 
magnetic. Cp.=FeCr, with some Fe replaced by Mg and 
some Cr by Al. Bp. infusible. With borax it fuses to a green 
globule. If fused with saltpetre and dissolved in water, it 
yields a yellow solution, which shows the reaction of chromic 
acid. Scarcely affected by acids. 

Chromic iron very frequently occurs as an accessory in 
serpentine (Islands of Unst and Fetlar, Shetland), rarely in 
dolomite (Hoboken, New Jersey). 

98. Hematite (Specular Iron, Red Iron-ore}. Rhombo- 
hedral ; in rhombohedrons, pyramidal or tabular crystals, 
which are singly imbedded or attached in groups (Specular 
Iron, Micaceous Iron), or subcrystalline, frequently fibrous in 
botryoidal, reniform, or stalactitic masses ; also granular, 
lamellar, compact, and earthy textures (Bed Hematite, Fibrous 
Red Iron, Scaly Red Iron, Red Iron Froth, Reddle, or Red Chalk, 
&c.) The crystallised varieties have : Cleavage basal and 
rhombohedral, imperfect. H.^5'5 6'5. S.G. = 4'5 5'3. 
Fracture conchoidal to uneven. Colour iron-black to dark 
steel- grey. Streak cherry- or blood-red. Lustre metallic. 
The subcrystalline varieties have: H.=3'5 only. S.G. 
4*5 4'9. Colour blood-red to brownish-red, sometimes pass- 
ing over into steel-grey. Streak blood-red. Lustre dull. 
Cp. Fe, sometimes with some Ti. Bp. both varieties become 
black and magnetic in the reducing flame. In acids but slowly 
soluble. 

Specular iron (eisenglanz) includes the varieties with perfect 
metallic lustre ; red iron-ore the amorphous varieties. The sub- 
crystalline varieties of hematite frequently contain impurities, 



ANHYDROUS OXIDES. 63 

siliceous, argillaceous, &c. Itabirite is a granular variety of 
the same mineral containing quartz, jaspery clay -iron ; reddle, 
argillaceous iron. Hematite forms independent rocks and 
beds, sometimes horizontally imbedded between the strata of 
other sedimentary rocks. It also forms an essential constituent 
of micaceous iron-gneiss and micaceous iron-schist. It is like- 
wise met with as an accessory in many other rocks. At Vesuvius 
and ^Etna it fills clefts in lava, or is found in vesicular cavities 
of lava, where it is probably the result of the decomposition of 
fumes of chloride of iron by the vapour of water (steam). In 
other cases it is usually a product of metamorphism from 
spathic iron and brown hematite. Again, it is sometimes pos- 
sibly a direct hydrogenic formation (especially where it is 
pseudomorphous of other minerals or dendritic on the surfaces 
of rock clefts). 

99. Titaniferous Iron (Titanic Iron-ore, Ilmenite, Crichtonite) . 
Rhombohedral, isomorphous with specular iron. Crystals 
imbedded singly, or attached in groups. Also massive, in 
granular lamellar aggregates, or dispersed in grains. Cleavage 
sometimes rhombohedral. Fracture conchoidal to uneven. 
H.=5 6. S.Gr.=4'5 5. Colour iron-black to brown or 
steel-grey. Streak black to brownish-red. Lustre semi- 
metallic. Opaque. Cp.=Ti and Fe in various and probably 
indefinite proportions, sometimes with some Mn, or Mg. It 
will be seen that this composition admits of a near approach to 
that of hematite, and in truth the division between the two is 
not very definitely marked. Bp. infusible, with fluxes gives 
the reactions of iron and titanium. If heated in concentrated 
sulphuric acid, it gives a blue colour. Soluble with difficulty 
in muriatic or nitric acid, titanic acid being separated. 

Titaniferous iron is an accessory ingredient in many rocks, 
especially in basalts and dolerites, also in talc-mica-schist 
(Gastein), miascite (Ilmensee near Miask), granite (Aschaf- 






64 MINERALS. 

fenburg). Very frequent in river deposits (Menaccan in 
Cornwall). 

100. Braunite. Dimetric. Crystals usually small and in 
pyramids resembling the octahedron, clustered in geodes and 
in granular aggregates. Cleavage pyramidal, tolerably per- 
fect. H.=6 6-5. S.G. =475 4-82. Colour iron-black to 
brownish-black. Streak black. Lustre metallic, resinous. 
Opaque. Cp. = Mn or MnMn. Bp. infusible. With borax, 
phosphor- salt, or soda gives the reaction of manganese. Soluble 
in muriatic acid, chlorine being evolved in the process. 

Braunite occurs sometimes as an accessory in other rocks, 
chiefly, however, in veins. (In the porphyry of Oehrenstock 
near Ilmenau, Elgersburg in Thuringia.) This mineral and 
similar manganese products very frequently form dendritic 
coatings to the faces of clefts in rocks. These dendritic forma- 
tions are usually exfiltrations from the mother rock. 

101. Hausmannite (JBraunstein) . Dimetric. Crystals always 
pyramidal, grouped in geodes. Cleavage basal, tolerably per- 
fect, pyramidal less distinct. H. = 5 5*5. S.G.=47. Colour 
iron-black. Streak brown. Lustre bright metallic. Opaque. 
Cp. = MnMn. Bp. like oxide of manganese. Soluble in 
muriatic acid, with disengagement of chlorine. In concen- 
trated sulphuric acid, after a short time, assumes a bright red 
colour. 

Hausmannite is usually found in separate beds (Ilmenau in 
Thuringia, Ihlefeld in the Harz), and would appear to be in 
almost all cases a hydrogenic product, Mn having been first 
dissolved in spring and other water, and having afterwards 
absorbed more oxygen from the air. Daubree has, however, 
shown the possibility of producing hausmannite by the reaction 
of water in the state of steam upon chloride of manganese at a 
red heat. 

102. Polianite. Trimetric. Crystals usually in short prisms, 



ANHYDROUS OXIDES. 65 

vertically striped. Also massive in granular aggregates. 
Cleavage brachydiagonal. H.=6'5 7. S.G-.=4'84 4'88. 
Colour light steel-grey. Streak black. Lustre black metallic. 
Opaque. Cp.=Mn. Bp. infusible ; on charcoal changes to 
brown MnMn. Soluble in muriatic acid, with brisk effer- 
vescence of chlorine. 

Pyrolusite is sometimes a modification of polianite, sometimes 
a product of the transmutation of manganite, a mineral which 
we shall presently notice. The manganite is a compound of 
Mn and water, and it has a strong tendency to part with its 
water and absorb oxygen. Polianite is frequently found in 
beds of the manganese- ores (Flatten in Bohemia, Johanngeor- 
genstadt, Saxony). Pyrolusite is found in the same localities, 
or associated with iron-ores (Siegen, in many parts of France). 

103. Cassiterite (Tin-ore, Tinstone). Dimetric. Crystals in 
short prisms or pyramids, very often twins, imbedded or at- 
tached ; also massive, granular, or fibrous (wood- tin). Cleav- 
age prismatic, imperfect. Brittle. H.=6 7. S.Gr.=6'3 7'1. 
Colour usually yellowish-, reddish-, or blackish-brown ; rarely 
colourless. Streak colourless or brownish. Lustre adaman- 
tine or resinous. Translucent to opaque. Cp. = Sn, usually 
with some Fe, Mn, Si, and Ta. Bp. unchangeable, on charcoal 
with carbonate of soda reducible to metallic tin. Not affected 
by acids. 

Tin-ore is principally found in metalliferous veins, also as 
an accessory, and especially so in plutonic rocks (greissen, 
granite, and tourmaline rocks). Wolfram, tourmaline, beryl, 
and topaz are almost always associated with this mineral. 

Tin-ore in nature is doubtless in many cases a product of 
wet processes (we find pseudomorphs after felspar in Corn- 
wall) ; but Daubree has also proved that crystallised oxide of 
tin may be formed by the action of steam on fumes of chloride 
of tin. 

F 



66 MINERALS. 

104. Rutile (Nigrine). Dimetric. Crystals always columnar, 
frequently very thin, acicular and capillary, imbedded and at- 
tached, frequently twins ; also massive, compact, or granular. 
Cleavage prismatic, perfect. Fracture conchoidal. H.=6 6*5. 
S.Gr.=4'18 4'25. Colour yellowish- or reddish-brown to black 
(nigrine). Streak yellowish-brown. Lustre metallic adaman- 
tine. Translucent to opaque. Cp.=Ti, with small quantity 
of Fe. Bp. unchangeable ; with borax gives reaction of 
titanium. Not affected by acids. 

Rutile occurs only as an accessory ingredient in rocks ; 
chiefly in greenstones and diorites, rarely in granite ( Warwick 
in America) ; gneiss and mica-schist (Barre and Shelburne in 
Massachusetts) ; or in granular limestone (Edenville in New 
York). 

Daubree has produced crystallised titanic acid by the action 
of steam upon fumes of chloride of titanium. 

(&) HYDROUS OXIDES. 

105. Manganite. Trimetric, sometimes hemihedral. Crys- 
tals always columnar and distinctly marked with vertical 
stripings, frequently grouped in bundles or clustered in the 
form of geodes. Also massive in fibrous, divergent, rarely in 
granular aggregates. Cleavage, brachydomatic very perfect, 
basic and prismatic imperfect. Somewhat brittle. H. = 4. 
S.G.=4'2 4*4. Colour dark steel- grey to nearly iron-black, 
frequently brownish-black. Streak brown. Lustre imper- 
fectly metallic. Opaque. Cp. MnH. Bp. in matrass yields 
water, with borax gives reaction of manganese. Perfectly 
soluble in concentrated muriatic acid, chlorine being disen- 
gaged. Slightly soluble in sulphuric acid, which colours it 
pale red. 

Manganite is found in separate beds with other manganese- 
ores (Ihlefeld in the Harz, Ilmenau and Oehrenstock in 



HYDROUS OXIDES. 67 

Thuringian Forest). We have already noticed the tendency 
of manganite to change into pyrolusite. 

Psilomelane and Wad are two hydrous ores of manganese, 
occurring frequently with other manganese ores, or as acces- 
sories in rocks. They are crystalline, also amorphous, some- 
times massive, in reniform, stalactitic, lamellar, and earthy 
varieties. Cp. (of psilomelane) = RMn 2 + H, with Mn, Ba, 
K ; (of wad) very variable, so that it is hardly to be called an 
independent mineral : consists principally of Mn, Mn, and 
H, with variable proportions of Ba, Ca, Cu, Co (earthy cobalt 
or asbolan). 

106. Limonite (Brown Iron-ore, Brown Hematite). Subcrys- 
talline. In fibrous masses of globular, reniform, or stalactitic 
shape. Also compact or earthy. H. = 5 5*5. S.G.=3*6 4. 
Colour, clove-brown to yellowish- or blackish-brown, black. 
Lustre silky, shining or dull. Opaque. Cp. = Fe 2 H 3 . Bp. 
becomes black and magnetic, is fusible in thin laminae. With 
borax it gives reaction of iron. Soluble in heated nitric 
acid. 

Limonite is a very abundant mineral, sometimes in inde- 
pendent beds, sometimes as an accessory. 

Gothite or Stilpnosiderite (FeH) is a mineral very closely 
allied to limonite and frequently associated with it. 

ii. Fluorides and Chlorides. 

107. Common Salt (Rock-salt). Monometric. Crystals 
always cubic ; usually in granular or fibrous aggregates or 
massive. Cleavage cubic, very perfect. Fracture conchoidal. 
Slightly brittle. H.=2'5. S.G.=2'1 2'2. Colourless or 
grey, or yellowish, or reddish ; rarely blue or green. Lustre 
vitreous. Transparent. Taste pure saline. Cp.=NaCl, 

very often impure, containing F, Br, KC1, MgCl, and other 

F 2 



68 MINERALS. 

salts. Soluble in 3" 7 parts of water. Liquefies on exposure 
to moist atmospheres. Bp. decrepitates in matrass ; fuses on 
charcoal and evaporates with strong heat ; tinges the flame 
reddish-yellow, and if combined with microcosmic salt and 
oxide of copper, it gives a beautiful blue flame. 

Rock-salt is frequently met with as an independent rock in 
sedimentary formations of every age. It also occurs as an 
accessory ingredient in clay marls of the salt mountains 
(Berchtesgaden) where it is in the form of cubic crystals 
porphyritically imbedded. In each case it is a neptunian 
product. It is found in a state of solution in sea- water, which 
contains about 2'5 per cent .of salt. It occurs in the steppes, 
in the sand of the Desert, in inland springs and lakes, and 
finally as a sublimation at the craters of volcanos. We shall 
have occasion to mention rock-salt again amongst the rocks. 

108. Sal-ammoniac. Monometric, usually in uncrystalline 
crusts, stalactites, or as an earthy coating. The crystals have 
conchoidal fracture. H.=l 1'5. S.Gr.=l'5. Colourless, or 
coloured yellow or brownish. Taste saline and pungent. Cp.= 
NH 4 C1. Easily soluble in water. Bp. in matrass evaporates 
entirely ; with soda emits a strong smell of ammonia. If 
melted with phosphor-salt and oxide of copper, it colours the 
flame a beautiful 1blue. 

Sal-ammoniac occurs as a product of sublimation in the 
clefts and fissures of volcanic rocks, and many lavas, also in 
burnt seams of coal. 

109. Fluor (Fluor-spar). Monometric, Cubic form very 
frequent. Crystals single or in groups, attached, also massive, 
in coarse granular and radiated aggregates, or amorphous and 
earthy. Cleavage octahedral, perfect, so that the conchoidal 
fracture is seldom observable. Brittle. H. = 4. S.Gr.= 
3'14 3'19. Colour blue, yellow, green, and various. Some- 
times colourless and limpid. Lustre vitreous. Transparent, 



FLUORIDES AND CHLORIDES. 69 

translucent, opaque. Cp.=CaF. Bp. decrepitates violently, 
shows phosphorescence, and in thin laminae fuses to a clouded 
mass, tinging the flame red. In a stronger flame the fused 
product becomes infusible, and acts like lime. Is completely 
decomposed by concentrated sulphuric acid, giving forth hydro- 
fluoric acid. 

Fluor-spar forms independent rocks of subordinate extent. 
It occurs most frequently in metalliferous veins, from which it 
has occasionally spread into the mother rock. In dolomite it 
sometimes occurs as an accessory (St. Gotthard), and in geodic 
cavities of the variegated sandstone at Waldshut. It is also 
met with as a recent deposit from springs of water (Plom- 
bieres). The last mentioned case proves that fluor-spar may 
be produced by purely wet chemical process. 

110. Cryolite. Trimetric (?). Hitherto only known in 
amorphous single masses or thick crusts of coarse granular 
texture. Cleavage basal, tolerably perfect. Brittle. H.= 
2'5. S.G.=2'9 3'0. Colourless, greyish- white, or reddish. 
Lustre vitreous, on the basal cleavage face mother-of-pearl. 
Translucent. Cp.=NaF+Al 2 F 3 . Bp. very readily fuses to a 
white enamel, tinging the flame reddish-yellow. In glass tube 
gives the reaction of fluor ; on charcoal also it fuses easily, 
but is decomposed, and leaves a deposit of alumina. In con- 
centrated sulphuric acid it is perfectly soluble, giving forth 
hydrofluoric acid. 

Cryolite occurs in a separate bed or layer in the gneiss of 
Arksutfiord in West Greenland. 

in. Sulphurets. Arseniurets. 

111. Galena (Blue Lead-ore). Monometric. Very usual in 
cubes, more rarely in rhombic dodecahedrons, octahedrons, 
and other forms. Crystals usually attached, clustered in 
geodes, also botryoidal and reniform. Chiefly massive in coarse 



70 MINERALS. 

and fine grained or compact aggregates. Cleavage cubic, very 
perfect. Sectile. H.=2'5 275. S.G.=7'25 77. Colour 
lead-grey, sometimes with tinge of reddish colour, sometimes 
iridescent on the surface. Streak greyish-black. Lustre me- 
tallic. Opaque. Cp.^PbS, with frequently a small quantity of 
silver, or also of Fe, Se, Sb. Bp in glass tube, evolves sulphur 
and a sublimate of PbS. On charcoal decrepitates, fuses after 
the sublimation of the sulphur, and finally yields a lead globule 
and lead fumes. Soluble in nitric acid, with development of 
nitrous acid and precipitate of sulphur. 

Galena is met with as an accessory in many rocks, e.g. 
sandstones (in the form of disseminated grains Commern in 
the Eifel) ; in the argillaceous sphserosiderite of the Coal for- 
mation, and elsewhere. Very frequently in veins of ore (in 
the gneiss of Freiberg, in the Devonian strata of the Harz, 
in mountain limestone of Derbyshire and Cumberland, in 
granite of Linares) ; also in nests and irregular masses im- 
bedded, which are usually met with in limestone or dolomite 
(Tarnowitz in Silesia, Bleiberg in Carinthia, Alpuj arras in 
Spain). 

Although galena may very frequently be of hydrogenic 
origin, it is not less certainly in many cases a product 
of sublimation ; artificially it is formed in the cracks of 
furnaces. 

Gralena has given rise to many secondary products, such as 
cerusite (PbC) ; pyromorphite (3Pb 3 P + PbCl) ; and mime- 
tisite (3Pb 3 As + PbCl). 

112. Blende (Zincblende, Sphalerite). Monoclinic, tetra- 
hedral. The crystals frequently irregularly twisted, some- 
times twin growth ; often massive, in granular, rarely in 
fibrous or radiated aggregates. Cleavage very perfect ac- 
cording to the rhombic dodecahedron. Very brittle. H.= 
3'5 4. S.Gr. = 3*9 4'2. Colour, most frequently brown or 



SULPHURETS. ARSENIURETS. 71 

black, more rarely yellow-red, white or colourless. Lustre 
adamantine to resinous. Semi-transparent to opaque. Cp.= 
ZnS, sometimes combined with considerable quantities of FeS 
(up to 23 per cent) and a little cadmium. Bp. decrepitates 
violently, but is only fusible at the sharp edges. On charcoal 
in the oxidation flame gives zinc fumes. Soluble in concen- 
trated nitric acid, with precipitate of sulphur. 

Its place and mode of occurrence in nature are similar to 
those of galena, which is almost always associated with it. It 
has been likewise found in the cells of ammonites of the 
brown Jura and Lias formations, a fact which proves its partial 
formation by wet processes. 

113. Cinnabar. Bhombohedral. Crystals in rhombohedrons 
or thick tabular, small and in geodes. Usually massive, in 
granular, compact or earthy aggregates, dispersed or incrust- 
ing. Cleavage prismatic. Fracture uneven and splintery. 
Sectile. H.=2'25. S.G. = 8'99. Colour cochineal-red and 
scarlet ; streak scarlet. Lustre adamantine. Translucent ; 
opaque. Cp. = HgS. Bp. in matrass burns black; in open 
tubes sulphur burns with a blue flame, and sublimes, yielding 
fumes of sulphurous acid with black sublimate and a mirror 
of metallic mercury. Soluble in nitro-muriatic acid (aqua 
regia). 

Cinnabar forms independent beds, appears as impregnation 
of bituminous shale, or in veins (Idria), also forms incrustation 
on clefts of many kinds of rock (granite, clay-slate). 

114. Magnetic Pyrites. Hexagonal ; m rarely crystallised, 
usually massive and disseminated, in lamellar, granular or 
compact aggregates. Cleavage basal, perfect ; prismatic im- 
perfect. Fracture conchoidal. H. = 3'5 4'5. S.G.=4'4 
47. Colour between bronze-yellow and copper-red ; streak 
grey-black. Magnetic. Lustre metallic. Opaque. Cp.= 
Fe 7 S 8 , sometimes contains Ni. Bp. unchangeable in matrass ; 



72 MINERALS. 

in glass tube gives out S, but no sublimate ; on charcoal fuses 
in reduction flame to a greyish black and highly magnetic 
bead. Soluble in muriatic acid, sulphuretted hydrogen being 
developed, and sulphur precipitated. 

Magnetic pyrites occurs with metallic ores, also as an acces- 
sory ingredient in many igneous rocks, especially diorite, in 
Vesuvian lavas and in meteorites. 

115. Pyrites (Iron Pyrites). Monometric, in various hemi- 
hedral combinations. Crystals singly imbedded, or combined 
in geodes and various groups ; also in globular and reniform 
or fibrous aggregates, or massive. Cleavage cubic, imperfect. 
Fracture conchoidal to uneven. Brittle. H.=6 6'5. S.Gr.= 
4' 8 5. Bronze-yellow to gold-yellow. Streak brownish- 
black. Lustre metallic. Opaque. Cp.=FeS 2 , with occasion- 
ally small quantities of Au or Ag. Bp. in matrass gives out 
sulphur and sulphurous acid, and afterwards acts like magnetic 
pyrites. Scarcely affected by muriatic acid. Soluble in nitric 
acid, leaving a precipitate of sulphur. 

Pyrites is found in independent beds. It is also an essential 
constituent of the species of granite called beresite. It is a 
very frequent accessory ingredient in many rocks ; very fre- 
quent in the crystalline schists, in diorite, limestone, in clay 
rocks, in coal. It is no less frequent in metalliferous veins. 

Pyrites is sometimes formed by the action of a solution of 
copperas on organic substances, and this will account for its 
often being found in the form of fossils. Wohler has produced 
artificial pyrites by slowly heating oxide of iron, together with 
sulphur and sal-ammoniac. 

116. Marcasite (White Iron Pyrites, Hydrous Pyrites). 
Trimetric. Crystals tabular or columnar, usually clustered 
into groups termed radiated pyrites, spear pyrites, hepatic 
pyrites, cockscomb pyrites, cellular pyrites, according to vary- 
ing texture. Cleavage prismatic, indistinct. Fracture uneven. 



SULPHURETS. ARSEXIURETS. 73 

Brittle. H. = 6 6-5. S.G.=4'6 4'8. Colour greyish bronze- 
yellow, inclined to green ; tarnishes very readily. Streak dark 
greenish-grey. Lustre metallic. Opaque. Cp. like pyrites, 
but more prone to decompose and turn to vitriol. Bp. like 
pyrites. 

Marcasite is found in separate beds, and as an accessory 
mineral (Browncoal formation of the Carlsbad region, dolo- 
mites of Tharandt in Saxony, and Cornwall). 

117. Leucopyrite. Trimetric, usually massive and dissemi- 
nated, granular, or fibrous. Cleavage basal. Fracture uneven. 
Brittle. H.=5 5'5. S.G. = 7 7'4. Colour silver-white, 
merging into steel-grey. Streak black. Lustre metallic. 
Opaque. Cp.=FeAs 2 , almost always with some sulphur, 
owing to admixture of mispickel. Bp. in matrass yields sub- 
limate of metallic arsenic ; on charcoal strong smell of arsenic, 
and a black magnetic residuum. Soluble in nitric acid, with 
a separation of arsenious acid. 

Leucopyrite is an accessory in many rocks, especially in 
serpentine (Reichenstein in Silesia), and in metalliferous veins. 

118. Mispickel (Arsenopyrite) . Trimetric. Crystals usually 
short prisms, or tabular, singly imbedded, or attached in 
groups; also massive, in granular or fibrous aggregates. 
Cleavage prismatic, rather distinct. Fracture uneven. Brittle. 
H.=5 - 5 5'6. S.G. = 6 6*4. Colour silver- white, inclining to 
steel -grey. Streak black. Lustre metallic. Opaque. Cp. = 
FeS 2 + FeAs. Several varieties contain Ag (Weisserz), Au, or 
Co (Kobalt-arsenkies). In matrass gives first a red, afterwards 
a brown sublimate of sulphuret of arsenic, finally a sublimate 
of metallic arsenic. On charcoal the arsenic is dissipated, and 
leaves a black magnetic bead, which acts like magnetic pyrites, 
and sometimes gives cobalt reaction. Soluble in nitric acid, 
with separation of arsenious acid and sulphur. 

Mispickel is frequently met with in veins of ore, is also an 



74 MINEKALS. 

accessory ingredient in many rocks, e.g. the crystalline schists 
(Kongsberg in Norway, Freiberg, Franconia in New Hamp- 
shire), and serpentine in various localities. 

119. Chalcopyrite (Copper Pyrites) . Dimetric. Tetrahedral. 
Crystals usually small, frequently of regular twin growth, often 
massive. Cleavage pyramidal, sometimes distinct. Fracture 
conchoidal to uneven. Unlike pyrites, is very little brittle. H.= 
3*5 4. S.G.=4'1 4'3. Colour brass-yellow, sometimes with 
tarnish of gold colour and iridescence. Streak black. Lustre 
metallic. Opaque. Cp.= Cu 2 S + Fe 2 S 3 . Bp. becomes black 
on cooling, red, and fuses at a strong heat to a magnetic bead 
of steel-grey colour ; with borax and soda gives a copper bead ; 
when moistened with muriatic acid tinges the flame a beautiful 
blue. Soluble in nitro-muriatic acid (aqua regia) with separa- 
tion of sulphur. 

Chalcopyrite is a very frequent associate of pyrites. Is 
accessory in many rocks, e.g. tourmaline-granite, Predazzo, 
Tyrol. 

iv. Native Elements. 

120. Sulphur. Trimetric. Crystals usually pyramidal, 
singly attached, or clustered in geodes ; also globular, reni- 
form, stalactitic ; with fibrous or compact structure. Cleavage 
basal and prismatic, imperfect. Fracture conchoidal to uneven, 
and splintery. Not very brittle. H.=1'5 2'5. S.Gr.=2. 
Colour sulphur-yellow to straw-colour, or yellowish-grey. 
Lustre resinous ; on crystal surfaces adamantine. Transparent, 
translucent. Cp. = S, frequently mixed with clay or bitumen. 
Bp. sublimates in matrass ; inflammable, and burns with blue 
flame to sulphurous acid gas. 

Sulphur occurs as an accessory in rocks, and also as a sepa- 
rate formation in beds. It is formed by sublimation in the 
clefts of volcanoes, also in the neighbourhood of burning coal 



NATIVE ELEMENTS. 75 

seams. Sometimes it is the product of the decomposition of 
metallic sulphurets, or of the sulphuretted hydrogen of some 
spring waters, which are decomposed by contact with the 
atmosphere, and form deposits of sulphur. 

Artificial crystals of sulphur may be produced in great per- 
fection by dissolving sulphur in sulphuret of carbon, and set- 
ting it to crystallise at ordinary temperature. Monoclinic crys- 
tals of sulphur, which have not as yet been observed in nature, 
are obtained on the cooling of melted sulphur. 

121. Graphite (Plumbago). Hexagonal, rhombohedral, usu- 
ally in six-sided, thin tabular or short prismatic crystals ; also 
massive, in radiated, lamellar, or compact aggregates. Cleav- 
age basal, very perfect, prismatic imperfect. Very sectile, 
flexible in thin laminae. Feel greasy. H.=l 2. S.G.= 
2 '09. Colour iron-black to grey. Streak black, with metallic 
lustre, soils paper, used for pencils to draw and write with. 
Opaque. Cp.=C, with some iron, and often containing im- 
purities of Si, Ca, and AL Bp. burns with difficulty . If heated 
with saltpetre, puffs up slightly. 

Graphite is sometimes found in separate beds, and is then 
probably the final product of the transmutation of vegetable 
remains. It is, however, also found as an accessory ingredient 
in igneous rocks (in trap at Borrowdale, Cumberland, in por- 
phyrite at Elbingerode in the Harz, in granite boulders, Green- 
land) ; in limestones (Lower Styria, Fichtelgebirge), or in 
metalliferous veins (Arendal) ; finally as an essential consti- 
tuent of graphite-granite, graphite-gneiss, graphite-mica-schist. 
The igneous origin of some graphite may be inferred from its 
presence in furnace slags, where it sometimes occurs in the 
form of thin lamiiui'. 



76 MINERALS. 

v. Eesins. Organic Compounds. 

122. Amber (Yellow Mineral Resin). It is exclusively found 
in rounded masses of the shape of drops or fluid substance, 
and frequently insects and fragments of plants are enclosed in 
it. Fracture perfectly conchoidal. Little brittle. H.=2 2 '5. 
S.G. = 1*1. Colour yellow or brown in various shades, fre- 
quently with flame-shaped pencilling^. Lustre resinous. Trans- 
parent, translucent. When rubbed,, becomes negatively electric. 
Cp.=C 10 H 4 0. Bp. fusible y burns with a clear flame, and 
agreeable smell. 

Amber is a fossil gum-resin, the product of conifers or ter- 
tiary lignites. It is found as an accessory in strata of the 
Upper Chalk formation (Lemberg), the planercoal (Skutschin 
Bohemia), in pebbles in the diluvium and alluvium of North 
Germany, on the coast of the Baltic, and of Yorkshire and 
Essex. 

123. Bitumen (Asphalte, Naphtha, Petroleum, Mineral Pitch, 
Mineral Oil). 

Under the term bitumen are included a whole series of olea- 
ginous and pitch-like substances, of which the most important 
are naphtha and asphalt e. 

(a) Naphtha, a volatile, and, when pure, colourless, oil with 
bituminous smell. S.G.=07 0'84. Cp.=C 6 H 5 , fre- 
quently mixed with paraffine, asphalte and the like. 

(6) Asphalte, a hardened mineral pitch without oil ; massive 
with perfect conchoidal fracture. Colour pitch-black. 
Lustre resinous. Opaque. When rubbed gives a 
strong bituminous smell. Cp. = C, O, and H in un- 
certain proportions. Easily ignited, burning with a 
bright flame and thick smoke. 
Naphtha flows from the ground in considerable quantities 



RESINS. ORGANIC COMPOUNDS. 77 

(Persia, Pennsylvania, Amiano in Parma, Canada, Cali- 
fornia, &c.). 

Asphalte is found in many localities (e.g. at the Dead Sea ; 
Trinidad, where there is a complete pitch-lake ; at Poldice in 
Cornwall it occurs in granite). 

An intermediate substance between naphtha and asphalte is 
elastic mineral pitch or elat&rite (Castleton in Derbyshire). 

All these bituminous substances are of vegetable or animal 
origin, partly products of distillation of organic remains. They 
frequently occur as admixtures in shales and other rocks, 
which have received the name of bituminous ( Autun in France, 
Bonn, Markersdorf in Bohemia, &c.) 

124. Mellite (Mellilite, Honey Stone). Dimetric, usually in 
pyramidal crystals, singly imbedded. Cleavage pyramidal, very 
imperfect. Fracture usually conchoidal. Somewhat brittle. 
H.=2 2-5. S.G. = 1'5 1-6. Colour honey-yellow to wax- 
yellow, seldom white. Lustre resinous. Semi-transparent to 
translucent. Cp. = A1(C 4 3 ) + 18H. Bp. it carbonises with 
smell of burning ; on charcoal burns to a white ash, which acts 
like pure alumina. It is readily and completely soluble in 
nitric acid. 

Mellite occurs as an accessory ingredient in Browncoal 
(Artern in Thuringia, Luschitz in Bohemia). 



78 ANALYSIS OF EOCKS. 



CHAPTER II. 

ANALYSIS OF ROCKS. 



MICKOSCOPIC ANALYSIS. 

IT not unfrequently happens that the various mineral 
ingredients of a composite rock are so small and inti- 
mately blended together as to be entirely undistinguish- 
able even to the practised eye unaided by magnifying 
power. A simple lens will often render great service in 
this respect, but the aid of magnifying power may be 
carried much further with the microscope. For the mi- 
croscope very thin plates of a rock, so thin as to be 
somewhat transparent, are cemented on glass, and by the 
aid of a powerful instrument, textures apparently quite 
compact are frequently resolved into a web of minute 
crystals, or we find individual crystals become prominent 
(porphyritic) in an actually compact matrix. The form of 
these minute crystals is sometimes to be recognised, and 
so serves as a guide to the determination of the mineral 
in doubtful cases. If we further call in the assistance of 
polarised light, we are enabled to pronounce, with greater 
certainty, on the amorphous or crystalline character of the 
compact mass, and on the character of the crystals which 
by these means are brought to view. 

Delicate investigations such as these no doubt require 
the assistance of complicated apparatus and demand time, 
so that they are quite out of the question for the geologist 
on his travels ; but as we have said, much may be dis- 
covered by a simple lens, which for the practical geolo- 
gical purposes of the general inquirer is in most cases 
sufficient. 

MAGNETIC ANALYSIS. 

An admixture of magnetic iron-ore makes many rocks 
magnetic in their entirety, so as to affect the magnetic 



CHEMICAL ANALYSIS. 79 

needle, or if the iron-ore be present in small quantities 
only, it may be discovered by abrasure with a sharp- 
edged magnet, the magnetic particles of the powder so 
formed clinging to the magnet like a beard. As, how- 
ever, magnetic iron-ore occurs in many very different 
rocks, its discovery does not often afford much help to the 
geologist in determining the character of any given rock. 
Fostemann and Delesse have made careful investiga- 
tions of the magnetism of many different rocks. The 
former is of opinion that by means of careful magnetic 
experiments, we ought to be able to ascertain whether a 
rock be of volcanic or neptunian origin, whether it has 
been rendered metamorphic by heat, whether it has re- 
tained its original position or been subsequently displaced 
(vide Poggendorff's Aimalen^ 1859, vol. cvi. p. 106). 
Delesse had previously discovered that almost all igneous 
rocks were somewhat magnetic as well as many sedi- 
mentary ana 1 metamorphic rocks. (Annales des Mines, 
1849, vol. xv. p. 1, and Bulletin de la Soc. Geol. de 
France, 1850, vol. viii. p. 108.) 



CHEMICAL ANALYSIS. 

The geological interest attaching to the chemical ana- 
lysis of rocks is chiefly in respect of the nature of their 
origin. 

In the early stages of the science the analysis of com- 
posite rocks was conducted by mechanically separating, 
as far as possible, their several mineral ingredients, and 
analysing each mineral species individually ; and this 
method is still sometimes adopted where the parts are 
very distinct and easily to be separated. Compact rocks, 
such as basalt, were mostly considered as simple mineral 
substances, and so analysed. When, however, it came to 
be recognised that many apparently homogeneous rocks 
were but mechanical compounds of several minerals, 
chemical analysis was directed to the discovery of these 
mineral constituents too intimately mixed to be distin- 
guished by the eye. 

Gmelin introduced the method of treating a powdered 
mass of rock with muriatic or other acid, and so sepa- 



80 ANALYSIS OF ROCKS. 

rating it into a part soluble, and another part insoluble in 
such acid. These two parts he separately analysed, and 
reduced the results into chemical formulas. The object 
he had in view was chiefly to discover the mineral con- 
stituents of the rock. But this mode of analysis is in- 
adequate for the purpose, since few minerals are wholly 
soluble, or wholly insoluble, in acids, and therefore, in- 
stead of the several minerals being separated from each 
other, a part of each is dissolved and a part of each left, 
and no definite result as to the original structure can be 
attained. It is found that even the elementary consti- 
tuents cannot be successfully so divided ; but that some 
elementary substances are only partly dissolved and partly 
precipitated by the process. Nevertheless, as a rough 
approximate, and somewhat empirical mode of suggesting 
rather than proving the constituents of a rock, it is still 
sometimes employed, and may in certain cases be of use. 

As the chemical character of minerals came to be better 
known, less reliance was placed on chemical analysis as 
a means of ascertaining and distinguishing the mineral 
ingredients of rocks. A small number of elements are so 
universal in their character that they enter into the com- 
position of a very large proportion of the whole series of 
mineral bodies, a very slight variation in their propor- 
tionate quantities or combination serving to produce en- 
tirely different minerals, or even the very same elements 
in the same relative quantities wearing a totally different 
mineral aspect according to slight differences in the con- 
ditions of their original formation. Therefore it is that 
chemical analyses have always hitherto failed, and it 
would appear that they must always fail, to detect many 
important mineral differences. 

For instance, a rock containing 72 silica, 11 alumina, 
2*8 oxide or protoxide of iron, 1 lime, 1*2 magnesia, 1*2 
potash, 2 soda, and 0*4 water, may either be a granite, or 
a gneiss, protogine, granulite, quartz-porphyry, felsite, 
petrosilex, pitch-stone, trachyte-porphyry, obsidian, or 
pearlstone ; and if we take a wider margin for the propor- 
tion of silica, say from 62 to 72, increasing some of the 
other ingredients in proportion, then a rock, such as we 
have described, may be a trachyte, phonolite, or minette, 
for in all the rocks we have named similar values of their 



CHEMICAL ANALYSIS. 81 

elementary constituents occur. Again, a rock, containing 
49 50 silica, 12 alumina, 5 10 oxide or protoxide of 
iron, 5 lime, 2 3 magnesia, 1 potash, 2 soda, and 1 
water might just as well be a dolerite as a basalt,, or a 
nepheline rock, leucite rock, diabase, diorite, gabbro, 
hypersthenite, melaphyre, or porphyrite, for in like 
manner those values occur in all these rocks. 

On the other hand rocks, the same in mineral composi- 
tion, may vary in the values of their chemical or elementary 
ingredients 10, 20, or even 40 per cent. 

The mineral character of rocks is therefore now sought 
to be determined in doubtful cases by microscopic rather 
than chemical analysis, or by tracing the different stages 
of a rock's transition from a compact into a distinctly 
composite state ; for many rocks (as we shall later have 
occasion to show) are found to pass by gradual stages 
from an apparently homogeneous mass into states where 
their mineral ingredients become distinctly and separately 
developed so as to be readily recognised. 

Whilst chemical analysis was thus found insufficient for 
determining the mineral character of a rock, it derived 
a new importance from the igneous theory of the consti- 
tution of the primary rocks, when these came to be con- 
sidered as the products of the consolidation of a general 
molten mass once the sole material of the earth's structure. 
The different minerals then came to be regarded as of 
subordinate importance in inquiring into the origin of 
rocks, and their differing forms of crystallisation or 
structure to be regarded but as accidental consequences of 
slightly different circumstances attending the consolidation 
of the formerly fused mass. 

In this view even the sum of a separate analysis (if it 
were possible) of all the minerals constituting a rock 
would fail to present a complete picture of its aggregate 
chemical character, unless the exact proportionate quan- 
tity of each mineral could be also ascertained, which is 
practically impossible, although it has been sometimes 
roughly attempted. 

These considerations led to the present mode of analy- 
sis, which is now usually adopted in the case of all rocks 
indiscriminately, whether compact or granular, homo- 
geneous or distinctly composite. This is what is termed 



82. ANALYSIS OF KOCKS. 

In German the ( Bausch analyse ' (or collective average 
analysis). It consists in pulverising a number of repre- 
sentative specimens carefully selected from various parts 
of the rock, and in mixing the powder thus obtained so 
thoroughly as to make the portion taken for the analysis 
a fair average sample of the whole rock. 

The results of these analyses are sometimes combined 
into chemical formulae such as those by which minerals 
are described. For instance : 

3(B)Si + 2KSi, 
or(R) 2 Si 3 



In such formulae we need hardly say there is always 
more or less of speculation or theory involved. 

The idea is to arrive at a view of the chemical consti- 
tution of the original molten mass, and chiefly in the first 
instance of the preponderance of the silica or other acid 
in the compound. In other words, the object is to ascer- 
tain if the original compound forming the rock, when in 
its previous molten state, were acidic or basic in its 
chemical character. It has been sought to express the 
same idea more simply by giving the proportion of the 
oxygen contained in the acids to that contained in the 
bases of the compound. Thus if, in a compound say of 
silica, alumina, peroxide of iron, potash and soda, the 
silica contain 3 parts of oxygen to 1 of silicon, and 
the alumina and peroxide of iron 1-J oxygen to 1 of 
aluminum and iron respectively, the potash and soda 1 of 
oxygen to 1 of potassium and sodium respectively, the 
oxygen quotient in a neutral compound would be 

3 : 11 I 1 

(a proportion which has been actually found to obtain in 
some rocks), and any variation of this proportion on either 
side would cause the compound to assume an acidic or a 
basic character ; thus, 

5 : 1J : 1 

would constitute an acidic compound, and 

3:312 

would constitute a basic compound. 

Bunsen endeavoured to set up two typical rocks, to be 



CHEMICAL ANALYSIS. 83 

termed the trachytic and the pyroxenic, the former con- 
taining much silica (acidic), the latter a preponderance of 
bases (basic). 

He endeavoured to bring all the igneous rocks under 
one or other of these two heads, but soon found many 
rocks of intermediate character. These he regarded as 
mixtures of the two, or rather as the result of a combina- 
tion of the two kinds of original material which he 
believed to have existed at their formation. 

He suggested the idea of the existence of two great 
furnaces in the interior of the globe, containing these two 
different mixtures in a molten state ; an idea which has, 
however, not met with much general favour or acceptance. 

Others have suggested, with more plausibility, that at 
the time when the whole earth was fluid, its component 
parts would be in some degree separated according to 
their specific gravity, and the silica being the lightest of 
the very abundant ingredients of the mass, would prevail 
in greatest quantity at and near the surface, so that the 
rocks which were first consolidated and the earlier volcanic 
rocks would be acidic, the next formed igneous rocks 
would be more basic, containing chiefly the lighter bases, 
such as alumina, potash, soda or lime ; whilst the latest or 
most recent igneous rocks would contain the least silica, 
and principally the heavier bases, e.g. iron. It has also 
been suggested that the older igneous rocks, as having 
been formed nearer to the surface of the globe, would 
probably contain more water than those of later origin. 

These, then, are the chief problems which have been 
suggested for solution by chemical means. The most 
simple and useful of the chemical differences is that of the 
varying proportion of silica. This quantity when ascer- 
tained forms a clue to the proportion of the other ingre- 
dients and general chemical character of the rock. Scheerer 
has lately proposed that all the igneous rocks should be 
divided into nine or ten classes, according to their quan- 
tity of silica, without regard to their mineral character. 

He has pointed out an easy mode of ascertaining the 
proportion by fusing the portion of the powdered rock 
selected for analysis with a certain proportion of carbonate 
of potash or soda (about five times its weight). So much 
of the silica as is more than the proportion required for a 

o 2 



84 ANALYSIS OF KOCKS. 

neutral compound will combine with the potash or soda of 
the carbonate salt, and drive off a proportionate quantity 
of carbonic acid so that from the quantity of carbonic acid 
so driven off, the quantity of silica contained in the 
original rock may be calculated. 

Without pronouncing on the correctness of any of the 
foregoing speculations*, we may however confidently say 
that for the purpose of lithological classification, an ex- 
clusively chemical grouping of rocks. would be utterly 
impracticable. How should the geologist pursuing his 
labours in the field, or on the mountain, wait for the 
tedious and uncertain process of a chemical analysis 
before naming the rocks which come under his ken ? We 
must, therefore, still adhere in the main to a mineralogical 
designation and nomenclature, and all the more, as in 
general we find the mineral characteristics of rocks very 
much coincide with geological phenomena. 

We need not, however, on this account disregard the 
results of chemical analysis, which are doubtless of the 
highest geological interest, and must prove of still greater 
value when they shall have been more fully and exten- 
sively carried out. 

We propose, moreover, to use these chemical properties 
for the purposes of our classification to the extent pro- 
posed by Bunsen of dividing the igneous rocks into two 
great classes, the acidic and the basic, merely warning 
our readers that there is, so far as our present knowledge 
extends, no rigid boundary between the two, and that 
the state of our analytical knowledge in general is still 
very imperfect. 

With these remarks we present the reader with the 
following extract from the analyses of Roth, as given in 
his masterly work on this subject ( e Gesteinsanalysen '). 
For the sake of brevity, the decimal figures have in some 
instances been omitted or shortened to one figure. 

* See post, pp. 367 et seq. 



CHEMICAL ANALYSIS. 



85 






ll 
Bi 


3 OJ 3 00 ^ ,-< <* f~ CO 

n j-iai 

eo 6 6 b 6 rH 4* 




j 


e<iot>. ^>^(Mf-H 

In id i 














1 


33 

ii 


<O CO <M -* <N M CO <M CN 

CO -H i-H rH 

1 II! 

O O i-i O O 

si 6 ^ - 


d' 


Syenitic 
Granite 


OOO -<*<oeokOOr-t 

t^(M rH r-l 

p o o o o o 

6 CO 6 6 H r^ f^H 


1 












I 


.3 N 


M 1 1 1 1 

00 CN rH 3 

*~ 66 rn 6 




I 


(N^O OS>*COOSOSOO 
<O <N rH 

,L iiiia 










S 


o o o o o e* o 

















il 


11 uu 

AH rH O ^-i W tH 




1 


t^-iOi-H (NeOi-HOOCO 

11 L.UU 










I 


6 <N rH 6 ^H A( ^H 


"3 












m 


is 

11 


T7 : 1 1 1 1 1 

O O ' -^ ^l CO ^H (M 

?t< OS O O O O O 

t^. 





1 


000 000 0.(N 

(M(>l6 6-^rH rHO 

:1 1 1 1 1 I 
J Ui 




1 


w5 ^i tooq-^t^b-^ 
II 1 1 1 1 







O CO r-t O CO 

t^ 




3 


1 1 1 

O O O O .-i O 
<N 00 ^-1 6 <N 

t>- 


* 


I 


I-HCO * (Mrjieooooco 

OO rH rH 

=U cliliJ, 




I 


0-*(N (N<MrH<MCOrH 
t^. I-H 
II 1 1 







i^ 6 66 6 

CO i t 




I 


U 4 4 

O -< i-H O 
t- i-H 




ill 

CO * W 
r- * S? 


t^rH CO OOCOrH^COrH 
CO C<l 

II 1 I 1 1 1 


\ 


.! 


<Mt^ QO-^(MW5CO^-' 
1 - i-H 
II II II 


5 

t 


B.SJ 
g'S 


ib 66 6 
rH 




5s 

'I 


1 1 II 1 

O O C< ( I-H Tj< ^ 

^ w 66 66 

CO 


H 


is 


CO-I-* CNCO<MOOOSCN 
O C^ rH 

1] iJ,iiJ, 




s 


rH t>- .t- (M <N 3 <N 

II 1 1 1 1 1 




5* 


99 9-^999 

OS (N rH O CO <M rH 

- 




I 


Mill 
oo o -< -* o * 













(NO r-l rH 






















1 




g 






1 






i 


!i 




o 


it 




c 
t 


& 

I 




~ 

o 
< 


I a 

_>> 


Jl -L 

.81 i 8!i35 

gq 5 3&& 


< 




Ji*i* 1- 

II I Nil 

i<J P^j ^^(^CCr^ 



86 



ANALYSIS OF EOCKS. 



Porphyrite 


11 J.^rlJ,cli 
IO rH 


Greywacke 
Sandstone 


P O rH CO p CO O 
TH O O O rH O C<1 
OO 

1 i I 1 1 1 

O O <M TH CSI CO 

ib o o o o o 


Melaphyre 


-MCOTH CMOCOCOCO(M 
CO <N rH i 1 I 1 

II Ml 

O O O rH p p 

TH O rH O rH rH 
kO rH 


Alum-Slate 


OOp O p p p TH p 

ib cc b cb cb M r~ o cb 

CO C<> 

II 1 1 1 1 1 

OO rH O rH CN O 

OO*O O rH O O <N 
TH rH 


if 


IT S ILII 


1 


>0 CO 00 <M CO rH t^ <M 1 

t^ CO rH rH rH rH 

II III 

O O rH 03 lO CN O 


w " 


lO TH lO (M O rH O 
TH rH 


6 


00 rH 




Oit^t>- ICrHrHrHCO'O 


. 


(M^OrH 5 <N TH iQ CO CO 


1 


ii i^iJ, 




1 1 MIM 

O O TH CO O O O 




CO 00 00 CO O rH O 

TH 




Oi CO O O (M rH C3 


Diorite 


COOOlM COOiOiCOt^rH 
CO rH rH 

u u^i 

CD (M b CO O <N O 
TH rH 


Argillaceous 
Mica-Schist 


C5 TH *O O rH CO CD Th TH 
t- <M rH rH rH rH 

II 1 II 1 1 
O O rH rH <M rH t- 

kO O3 O O O O O 


I 

1 
N 


O (M -J rH 
1 IJliJ 

O O O O O O O 


rnblende- 
Schist 


1!* H 7 i i 

p p *p p kp p c^ 




TH rH 


o 

w 


TH rH 


f-J 


H^ CO !> rH C^ ^O OO 00 C^ 

OO p p C<l O rH 
TH CO TH rH O rH O 


} 


OO GO OO TH rH CO CO 
I!" 1 = U 








OOO OOOrHrHO 


JL 

to 
o 


VO rH rH rH rH 
00 *0 t- 


if 


(M O O CDrHrHOOrH 

i r 7 

rH CO Jtr O5 


^ 


rH rH CO rH O (M O 
TH rH 





CO rH 


1 


iCiOQC rHCOCOTHOTH 

7> M C^ (M rH rH i 1 

O O O O TH rH lO 


1 


CO CO 

II Mill 

O O CO CO O CO 5 




CO !>. TH rH O O O 
CO 


N 


O O5 O O rH O O 


Dolerite 


t--COt>- COTHOSCO'OCO 

nrH rH i i 
O <O C^ O TH 
rH CO CO O O rH O 
TH 


Grey Gneiss 


H clidrU 






-02 




li 




Pg 




fe 


s^i-f? 1L 

l|^yi||i| 


METAMOR] 
SEDIMENTA 





s 



PHYSICAL STRUCTURE OF ROCKS. S7 



CHAPTER III. 

PHYSICAL STRUCTURE OF ROCKS. 



TEXTURE. 

BY the term texture, as applied to rocks, we mean 
chiefly their physical structure, having regard to the size, 
shape, and mode of adhesion of their individual mineral 
particles. All rocks may be divided into two principal 
classes, in respect of the size of their component parts. 
Either the separate mineral particles of which they are 
composed are large enough to be recognised as such by 
the naked eye, or they are so small as not to be dis- 
tinguishable in the general mass. In the former case 
rocks are termed granular, in the latter compact. The 
word granular is, however, usually only applied when 
the different mineral parts are all of a granular shape 
of nearly the same size, and are crystallised into each 
other. If on the other hand a rock consists only of 
grains, pebbles, or fragments mechanically cemented 
together, it is termed according to its character either a 
sandstone (arenaceous), a conglomerate, or a breccia, which 
terms we shall explain more at large hereafter. 

The term compact is usually only applied to a rock 
when its particles adhere firmly and closely together 
(without being fused into one mass like glass). If the 
particles only lie loosely together so that the mass is 
friable, then that condition is called earthy ; if they are 
intimately blended and fused into a homogeneous mass, 
then the state is termed vitreous or opalescent. The 
vitreous and opalescent conditions are indeed essentially 
different from the ordinary compact and earthy condi- 
tions, inasmuch as in the former no individual particles 



88 PHYSICAL STRUCTURE OF ROCKS. 

are found, whilst the latter at best are but very fine- 
grained. In extreme cases, however, this difference is 
only to be discovered with certainty by means of polarised 
light. 

Using the terms granular and compact in their 
wider sense, so as to include, on the one hand, the 
sandstones, conglomerates, and breccias ; and on the other 
the vitreous and opalescent rocks ; we may say that every 
rock must necessarily either be granular or compact 
that is to say, we either can, or cannot recognise their 
individual component parts. A rock, for instance, 
which is granular cannot at the same time, in the same 
part, be compact, and vice versa. These conditions are 
inconsistent with each other ; although transitions occur 
from one state to the other, and although the same 
mineral combination may at one place be granular and 
at another compact. 

In the case of composite crystalline rocks formed by 
the cooling of matter previously in a state of igneous 
fusion, the coarse-grained, fine-grained, compact, or 
vitreous state is probably the result only of a more or less 
speedy process of cooling. The slower the cooling pro- 
cess, the more time would be allowed for the mineral 
parts to form themselves into separate crystals, and the 
more coarsely granular would the rock become ; the more 
speedy the process, the more compact the rock would be, 
or if the process were very rapid, then the rock might 
even become vitreous. 

The latter condition is almost exclusively confined to 
those igneous rocks, which contain a large proportion of 
silica ; in such as contain but little silica, the compact and 
the vesicular state seem to be substitutes for the vitreous. 
If individual mineral particles occur in the form of dis- 
tinct crystals (porphyritically) in an otherwise compact 
mass ; then we may regard this as a sort of intermediate 
state between the granular and compact some of the 
mineral constituents, more prone to crystallisation than 
the rest, having developed themselves into crystals earlier 
and more vigorously than those. The very same dif- 
ferences of texture and condition may be frequently 
observed in the products of artificial melting at fur- 
naces. 



TEXTURE. 89 

In the case of compact rocks it is often very difficult to 
determine whether the undistinguishable particles have 
grown together in process of crystallisation, or are only 
mechanically bound together; whether they consist only 
of one mineral substance or a combination of several. 

AVe now proceed to consider the special kinds of tex- 
ture, structure, or state. 

The texture of a rock is termed PORPHYRITIC when 
distinct crystals or crystalline particles are distributed 
through an otherwise compact principal mass or matrix. 
The texture of the matrix or principal mass need not, how- 
ever, always be compact ; it may be crystalline-granular, 
or may exhibit many varieties of texture. Accordingly 
the porphyritic texture may be subdivided into 
(a) Porphyritic with compact matrix. Rocks exhibiting ( 
this texture are called, porphyries, independently of ' 
the character of their mineral ingredients. 
(Z>) Porphyritic with granular matrix. Rocks exhibiting 
this texture are not called porphyries, but only por- 
phyritic; such for instance as many porphyritic 
granites, with large crystals of felspar in the gra- 
nular matrix. 

(e) Porphyritic with shaly or schistose matrix. Mica- 
schist for instance, if it contains garnets, thereby 
becomes porphyritic. 

The crystals thus porphyritically disseminated in a rock 
may either belong to its essential constituents or they 
may be accessories only. 

SCHISTOSE (FOLIATED), SLATY (CLEAVED), SHALY 
(LAMINATED), FISSILE are terms expressive of different 
kinds of internal parallel texture of rocks. The German 
geologists have the one term ' Schiefrig ' for all these 
varieties of texture, the common element in all of which 
is their tendency to split in the direction of a given plane. 
This tendency may, however, be the result of very dif- 
ferent causes, viz : 

(a) By the parallel arrangement of certain minerals, such 

as mica, chlorite, talc, &c. eminently cleavable in 
one direction. Mica-schist is a rock of this 
character, and the texture is termed schistose or 
foliated. 

(b) By some cause or causes, not to be discovered by mere 



90 PHYSICAL STRUCTURE OF ROCKS. 

ocular observation, the invisibly small mineral con- 
stituents or particles of the rock are arranged so 
as to produce a fissility or cleavage in the direc- 
tion of a given plane, which very often cuts at a 
considerable angle the plane or curved surfaces of 
stratification. The rock itself has frequently a 
compact appearance. The ordinary roofing slate 
is an eminent instance of this texture, which is 
termed slaty texture or cleavage. 

(c) By very thin parallel superposition or lamination of 

the fine particles of the rock. Thus a fissile tex- 
ture is developed in mud deposits, whether of marl, 
clay, or sand. This is in truth nothing but a kind 
of stratification on a small scale. The thin layers 
of the rock are not in themselves of a fissile tex- 
ture. Ordinary flagstones are of this character. 
Or a similar texture may be occasioned by the 
parallel juxtaposition of thin plates or lenticular 
particles of the ingredients of the rock, thus for in- 
stance the laminated texture of certain browncoals 
may be traced to their construction from an accu- 
mulation of actual leaves of trees, and a similar 
texture of certain amygdaloids is owing to the shape 
and position of the amygdaloidal particles. 

These and similar textures more or less origin- 
ating in the act and mode of deposition, and all of 
which have a tendency to split in the direction of 
their bedding, are called laminated or shaly, the 
rocks themselves shales. 

(d) Occasionally two of the above descriptions of texture 

occur together ; fissile is a general term which 
may be applied to all or any of the above-named 
textures.* 

* When we wish to be precise, we speak of the ' foliation of schist J 
the 'cleavage of slate ,' and the l lamination of shale? Jukes. 

See Jukes's Student's Manual of Geology (2nd edit.), pp. 265277. 

See also Phillips's Manual of Geology (1855), p. 43, and in Glossary, 
under heads of slate, schist, shale, laminated, flagstone, fyc. 

See also Page's Advanced Text-Book, 3rd edit. pp. 74, 81 ; also in 
Glossary under heads slate, schist, fissile, laminated, flags, shale. 

See also Dana's Manual of Geology, pp. 71, 93, 95, 96, 100, 101, 

All the above-named authorities agree, with very trifling excep- 



TEXTURE. 91 

As respects the different causes of the above mentioned 
varieties of the fissile texture, we have seen that the thin 
stratification productive of the laminated texture is in- 
variably the consequence of the original construction of 
the rock. But if rocks exhibit a slaty texture, which is 
not parallel to their bedding, this must have another 
origin than stratification. 

According to the opinions of Sharpe, Haughton, Sorby, 
and Tyndall, slaty texture or cleavage, when not iden- 
tical with stratification, has in most cases been caused 
by pressure in one direction (viz. at right angles to the 
cleavage plane), applied to the rock either during or sub- 
sequent to its formation that is to say, during consolida- 
tion in the case of igneous rocks, during process of trans- 
mutation in the case of the crystalline schists, and after 
their deposition in the case of the sedimentary rocks, in 
which it therefore seldom coincides with the plane of 
stratification. (Vide Journ. Geol. Soc. of London, 
1848-1849, and Phil. Mag., 1856.) 

On the other hand, the conjecture of Poulet Scrope, 
that lamination and cleavage may have arisen from friction 
of some kind appears to us improbable. Nor can we 
subscribe to the view advocated by Sedgwick, in his 
otherwise masterly treatise on the structure of large 
mineral masses (Trans. Geol. Soc. 1835, vol. iii. p. 469), 
namely, that this texture is the result of a crystallising 
force, although his view has been partially adopted by 
Sharpe and Murchison. (Vide Siluria, edit. 1859, p. 34.) 

Many rocks exhibit, variously developed, a marked 
texture, consisting of parallel fibrous lines or particles, 
with a parallel linear arrangement, called by Naumann, 
Linear Parallelism. This linear parallelism is of two 
kinds essentially differing from each other. It is either a 
delicate zig-zag pencilling of slaty or schistose rocks, or 
an elongation or extension of the particles or vesicular 
cavities in one direction. 

The linear foldings or pencilling of frequent occurrence 

tions, in the nomenclature as laid down by Jukes, and which is 
adopted in this translation throughout. It is almost identical with 
that first proposed by Sedgwick in 1835. See his ' Structure of Large 
Min -ml .Masses' in'Trans. of Geol. Soc. of London: 2nd series, vol. 
iii. p. 480. TRANSLATOR. 



92 PHYSICAL STRUCTURE OF ROCKS. 

in gneiss, mica-schist, and clay-slate have the appearance 
of having been occasioned by lateral pressure, although 
such an explanation of the phenomenon is open to great 
and various difficulties. Transitions are found from the 
most delicate pencilling to the coarsest foliation. 

Linear elongation or fibrous texture consists of a 
kind of an apparent extension or elongation of individual 
parts, or of all the particles of a rock in one principal 
linear direction, by which a texture resembling the fibres 
of wood is sometimes occasioned ; or else the vesicular 
cavities of a rock, either empty or filled (amygdaloids) 
are elongated in one prevailing direction. In the latter 
case, we may easily explain the origin of the texture by 
supposing the mass of the rock, during the period of its 
consolidation and whilst yet soft, to have been flowing in 
one direction. But it is much more difficult to ascribe a 
cause to the linear extension of the particles in other 
rocks, as, for instance, in some kinds of gneiss. 

VESICULAR, SconiACEOUs(or Slaglike\ PUMICEOUS, 
are textures of rocks containing cellular cavities more or 
less rounded, and which are evidently the result of 
gas bubbles, developed whilst the rock was in a soft 
state either at the time of its original formation, or at 
a subsequent period. If these cavities are only few and 
isolated, then the rock is termed vesicular. If, however, 
they are so numerous as to occupy an equal space with 
the solid part of the rock, then the texture is scoriaceous, 
and if the hollow part predominates over the solid, then 
pumiceous (bimssteinartig). The shape of the cellular 
cavities is most usually irregular, but sometimes very re- 
gularly spherical, or pear-shaped, lenticular, and occasion- 
ally the cavities are uniformly elongated in a particular 
direction, as if stretched. All these differences of shape 
may be easily explained by the circumstances under 
which the vesicular mass attained its solid state, whether 
it was in a state of quiescence, or was subjected to pres- 
sure, or whether it was in motion, and whether such 
motion was flowing or irregular. 

This vesicular condition is most frequently found in 
those igneous rocks which possess a compact, or at least 
a very fine-grained or porphyritic principal mass occasioned 
by rapid cooling. It never occurs in coarse-grained 



TEXTURE. 93 

igneous rocks, probably because these being always sub- 
jected to a high pressure, crystallised very slowly. But 
even sedimentary and metamorphic rocks sometimes con- 
tain genuine vesicular cavities, in which case we must 
always infer the rock to have been in a soft state during 
the development of the gas which caused the bubbles. 

Many rocks are porous without being vesicular, that is, 
they are penetrated with irregular and often even angular 
cavities, not the consequence of the development of gas, 
therefore not to be termed vesicular. The differences 
between porous and vesicular textures are sometimes very 
difficult to determine. 

To a certain extent almost all rocks are porous, 
although not so to the naked eye, in the sense that they 
admit of the percolation of water, even if but slowly. 
Daubree has made many experiments upon this kind of 
porosity, the result of which is communicated in the 
Bullet, de la Soc. Geol. de France, 1861, vol. xviii. p. 183, 
and Delesse has investigated the moist condition of rocks 
arising from this cause. (Ibid. vol. xix. p. 64.) 

A rock is said to be AMYGDALOIDAL when the vesicular 
cavities are filled either wholly or in part with new 
mineral substance. The filling of these cavities is always 
a process subsequent to the formation of the rock. The 
material for this purpose appears, as a rule, to have been 
derived from the rock itself by a species of exfiltration, 
and usually consists of chalcedony or quartz, or different 
kinds of carbonic spars or zeolites, or sometimes of green- 
earth, varying according to the character of the rock itself. 
The arrangement of these mineral substances is often very 
interesting ; concentric or horizontal layers, stalactites, and 
stalagmites, are formed within the cavities, or we find a 
crystallised geode or a compact mass. 

We infer from all the attendant circumstances that the 
formation of these amygdaloids must have been a very 
slow process, and therefore have occupied a considerable 
time in their completion. Hence, we may explain the fact 
that the most recent of all the igneous rocks, the lavas, 
although they are very often vesicular, are never amygda- 
loidal ; whereas the frequency and completeness of the 
filling up of the cavities increases almost in direct ratio 
with the age of the rock. 



94 PHYSICAL STRUCTURE OF ROCKS. 

Such igneous rocks as are rich in silica are not only less 
frequently vesicular, but their cavities, when they occur, 
are less frequently amygdaloidal than those with little silica 
in their composition, which probably arises from their con- 
taining fewer soluble substances adapted to the formation 
of amygdaloids, in particular, less lime and magnesia. 

There are some appearances which may be easily mis- 
taken for the amygdaloidal texture, but which only arise 
from a concretion of separate mineral parts without 
previous cavities. We shall mention these below under 
the names of spherulite, globuliferous, nodular) and 
variolitic. 

OOLITIC texture is only found in limestones and iron- 
stones, and it consists either in the entire mass being 
composed of small globules, or a great number at all 
events of such being contained in the mass. The glo- 
bules are very much of the size and shape of peas or 
grains of millet or lentils, and when broken exhibit a 
concentric or radiated structure. Sometimes many very 
small globules combine to form a larger ball. In the so- 
called roestune the globules are grey, and usually inter- 
nally compact, or somewhat radial in the common oolitic 
limestone or oolite. They are more frequently white or 
yellowish, and sometimes formed of concentric layers, or 
they show an organic origin. In pisolite or peastone they 
sometimes contain a nucleus of foreign substance, covered 
with concentric layers or coatings of calc sinter, and these 
layers also show a fibrous radial structure, so that we may 
distinctly recognise the process of structure to have been 
a repeated coating of a grain of sand. 

In oolitic ironstone the grains are partly spherical, 
partly lenticular. In bog-ore they exhibit a concentric 
structure, and sometimes attain considerable size, culmi- 
nating in reniform iron-ore. 

The origin of this texture is only to be recognised with 
certainty in the case of pisolite ; in the other similar 
formations it is more or less wrapped in obscurity, and 
especially in the Great Oolite beds it is still very pro- 
blematical. L. von Buch observed a kind of oolite for- 
mation on the shores of the Canary Isles very analogous 
in its apparent origin to the pisolite. Virlet d'Aoust 
found a species of oolite in the Gulf of Mexico produced 
by the coating of minute insects' eggs with lime (Comptes 



PARTICULAR STATES OF ROCKS. <J5 

Rendus, 1857, vol. xlv. p. 865). Some recently formed 
limestones, on the surface of coral reefs, are occasionally 
oolitic. Many oolites appear to be formed entirely of 
small and almost spherical shells (these are strictly speak- 
ing not genuine oolites). Deicke communicated a careful 
observation of the texture of roestone in the Zeitschrift 
f. d. ges. Naturw., 1853, p. 188, and more recently in the 
Transactions of the Lyons Academy, 1853. Fournet 
published a comprehensive treatise ' Sur la Formation des 
Oolites Calcaires.' 

In many of these rocks it would appear that the round 
grains are, in fact, only the result of a peculiar concretion 
of the homogeneous mass. 

SPHEKULITIC, or GLOBULIFEROUS (Dana). A tex- 
ture so named, somewhat similar to the oolitic, occurs in 
some felsitic igneous rocks, most distinctly in pearlstone. 
The round grains consist of pearl-like globules, or simply 
of compact felsitic concretions. 

Another variety of a similar texture sometimes occurs 
in basalt, dolerite, or phonolite, where it appears that the 
rock by a singular process of decay has resolved itself 
into grains of a tolerably round shape. 

NODULAR texture is closely allied to the oolitic, or some- 
times to the porphyritic, and consists in this that the 
mass of the rock contains small rounded or lenticular 
or somewhat elongated concretions of a firmer and more 
compact substance than itself. Under certain circum- 
stances this appearance is termed spotted, variolitic, or 
pock-marked. 

There also occur in rocks, but in a very subordinate 
degree, those states which in minerals are termed SPARRY, 

FIBROUS, Or ASBESTIFORM. 

PARTICULAR STATES OF ROCKS. 

There are certain states or conditions (in part identical 
with the above-mentioned textural phenomena) which, 
although they frequently alter the very nature and 
properties of the rock into which they enter, are never- 
theless not always considered a sufficient reason for 
giving a distinct name. This is not a consistent mode 
of treatment, for there are many cases in which rocks 
of precisely the same essential - mineral constituents 



96 PHYSICAL STRUCTURE OF ROCKS. 

are called by different names, by reason only of a dif- 
fering texture ; and, again, in cases where a series 
of rocks form a long but gradual chain of transition or 
gradation between two extremes of different character, it 
is the custom to give distinct names to many members 
of the series arbitrarily selected, and which can only be 
regarded as links in the chain. Still more inconsistent is 
it when the same conditions or properties are used in one 
case as a reason for a distinction, and in another not. 
But if we would avoid these and similar inconsistencies, 
we should be compelled to throw over the existing nomen- 
clature of rocks altogether, and substitute an entirely new 
one, which would be more hazardous than the inconsis- 
tencies themselves. 

We will now proceed to describe the most important of 
these special states in rocks, only observing in the outset 
that the terms used for denning the mere states are fre- 
quently also used more generally to designate the rocks 
themselves, and they sometimes even embrace a number 
of different rocks. 

1. Lava is not a definite rock, but is the name given to 

every rock which has been originally poured forth 
from a volcano in a state of igneous fusion. Thus 
we distinguish dolerite-lava, basalt-lava, trachyte- 
lava, &c. 

2. Wacke is the name given to a somewhat decomposed 

state of igneous rocks poor in silica. The mass 
has become more or less soft, almost earthy, of a 
yellowish or brown colour, and its mineralogical 
structure quite unrecognisable and only to be 
traced by transitions from the fresh state of the 
original rock. In subsequent pages we shall have 
occasion to speak of dolerite-wacke, basal t-wacke, 
melaphyre-wacke, greenstone-wacke, &c., or we 
shall use the adjective ( ivackenitic' * to designate 
this state of those rocks (wackenitic dolerite, &c.) 

3. Porphyry is the general designation for all porphyritic 

rocks with compact main mass or matrix, whereas 
those with a granular matrix are only termed por- 

* We have here been compelled to coin an adjective for the Ger- 
man ' wackenartig,' an equivalent for which we have been unable to 
find in English text-books. In analogy to porphyritic, granitic, &c., 
we trust the term may meet with acceptance. TRANSLATOR. 



PARTICULAR STATES OF ROCKS. 97 

phyritlc. Therefore we distinguish between quartz- 
porphyry, mica-porphyry, trachyte-porphyry, and 
porphyritic granite, trachyte, <fcc. The quartz- or 
felsite-porphyries however (with compact felsitic 
matrix) are frequently, par excellence, termed por- 
phyries without further designation. 

4. Amygdaloid (Mandelstein, Germ.) is the name given 

to every rock originally vesicular, whose cavities 
have in course of time become filled with mineral 
substance; hence there are basalt-amygdaloids, 
melaphyre-amygdaloids, &c. 

5. Scoria or Volcanic Slag, Scoriaceous, Slag-like, are 

terms expressive of' very open cellular states of 
basalt, trachyte, or other volcanic rock. 

6. Pumice, Pumice Stone, Pumiceous. These terms are, 

properly speaking, only expressive of the state or 
condition of certain rocks ; but this state is, ge- 
nerally speaking, confined to three kinds of rock 
trachyte, trachyte-porphyry, and obsidian, whose 
composition is essentially one and the same. 

7. Schist, Slate, Shale, are general terms for rocks con- 

sisting of very different mineral ingredients. The 
individual rocks are distinguished accordingly, e. g. 
as mica-schist, chlorite-schist, &c.,or clay-slate, &c., 
or bituminous shale, argillaceous shale, &c. ; or the 
adjectives schistose, slaty, shaly, are used in con- 
junction with the mineralogical name of the rock. 

8. Sandstone, Arenaceous, are general terms applied to 

rocks, consisting of a mechanical compound of small 
rounded or sometimes angular siliceous grains, 
usually quartz. 

9. Conglomerate is the universal designation for rocks 

consisting of rounded stones or pebbles, mechani- 
cally bound or cemented together. 

10. Breccia is a general term for rocks consisting of 

angular fragmens, mechanically cemented together. 

11. Tuff, Tufa. These terms doubtless in the first 

instance were used to express a loose, or little 
adhesive state of rock. 

Tufa is now principally used to denote an earthy 
compound of volcanic products of the most various 
kind, and 

H 



98 PHYSICAL STRUCTURE OF ROCKS. 

Tuff is chiefly applied to certain calcareous or 
siliceous deposits at the mouths of springs, very 
porous, and frequently very firm and tenacious ; 
in which case they are termed travertine. 
The four last states in the preceding list are also uni- 
versally made use of as separate classes of rock in them- 
selves, and as such they cannot indeed be well dispensed 
with, unless we would give separate names to each of the 
endless variety of rocks in each of those states ; a task 
not easily possible, nor are the varieties of rocks them- 
selves of sufficient importance to deserve such distinction. 

CONCRETIONARY STRUCTURE. 

A molecular arrangement quite distinct from crystal- 
lisation causes clusters of particles to segregate themselves 
round centres, or otherwise present various and singular 
appearances and shapes, which have received different 
names. 

Spherical concretions, which are very different from 
conglomerates, are frequently found in sandstones, clay 
rocks, marls, limestones, dolomites, quartz-porphyries, 
pitchstones, and greenstones. This structure has given 
rise to various names the oolite is an instance, so 
called from the egg-shape of the concretions ; pisolite 
is so called from its pea-shaped concretions, &c. Many 
concretions are compact, others are hollow, and their 
interior is sometimes garnished with crystals forming what 
is called a geode, a little crystal grotto ; or sometimes a 
small concretion is found loose in the hollow interior of 
the larger one, so as to rattle in it when shaken (clapper- 
stones). Some concretions are grouped together like 
clusters of grapes, or in irregularly kidney-shaped masses. 
These pass over into the nodular or massive concretions 
(Germ. Steinwulste, Schlangensteine, Lb'sskindel, &c.). 
Others are lenticular in shape, and are called swellings, 
or septaria. The latter is the special designation for 
lenticular concretions irregularly cleft in their interior, 
and frequently into pentagonal clefts on the outside. 
The clefts are frequently filled again with new mineral 
formations such as calcspar, brownspar, or ironspar. If 
their surface be exposed and much washed away by water, 



CONCRETIONARY STRUCTURE. EXTERNAL STRUCTURE. 99 

it sometimes occurs that the veins of spar, as being harder 
than the coating of the concretion, protrude and show a 
kind of network. 

These singular structures have been well described by 
Ehrenberg, Parrot, and Glocker with engravings. Ex- 
tracts from the treatises of Ehrenberg are to be found in 
v. Leonhard und Bronn's Jahrbuch, 1840, pp. 680 and 
741. The treatise of Glocker on the Laukasteine ap- 
peared in Breslau, 1854. 

Stylolites are a very singular formation in certain lime- 
stones, dolomites, or marls ; they consist of irregular and 
longitudinally striped cylinders standing at right angles 
to the rock's stratification, and often ended abruptly. 
Quenstedt endeavoured to explain their origin by sup- 
posing them to consist of spaces left by marine animals 
which had risen perpendicularly in the rock whilst yet 
soft, the tubes or spaces so formed being afterwards refilled. 
(See von L. und B. Jahrbuch, 1837, p. 406.) 

Cone in Cone. Concretions of a conical shape marked 
with concentric rings, are sometimes to be found in certain 
marls or marly limestones (in German these concretions 
are called Tuten, and smaller and more pyramidical con- 
cretions of the same kind are termed Nagel). 

No satisfactory explanation of the last three singular 
forms of concretion has yet been given. 

SPECIAL FORMS OF EXTERNAL STRUCTURE. 

There are certain other phenomena of rock structure 
(chiefly of their outward structure) which should not re- 
main entirely unnoticed here. We will, therefore, pro- 
ceed to mention them, merely premising that they are 
incapable of systematic arrangement, being individual in 
their character and unconnected with each other. 

Stalactites are formations produced in caverns or vesi- 
cular cavities after the manner of icicles, and resembling 
them in form. They are caused by the dropping of 
water holding some mineral in solution, and leaving 
behind a deposit or incrustation thereof. The mineral is 
usually calc-spar, barytes, aragonite, chalcedony, brown 
hematite, manganese spar, pyrites, or the like. If the 
incrustations, on the other hand, have been formed on the 



100 PHYSICAL STRUCTURE OF ROCKS. 

floor of the cavern or cavity by the drops when fallen, 
and have so grown upwards, they are called Stalagmites. 
Both stalactites and stalagmites are frequently met with 
in caverns of limestone and dolomite, where they are 
occasionally developed in extraordinary beauty and size. 
In vesicular cavities they are similarly formed, but of 
course smaller in size. Their original, normal position is 
necessarily perpendicular. If they are found in any other, 
that is the consequence of movement during or subse- 
quent to their formation. 

Dendrites (Dendritic) are terms applied to certain ex- 
ternal crystallisations or deposits, usually arborescent in 
form, which are found incrusting the surfaces of joints 
and fissures in many rocks. These dendrites usually 
consist of oxide of manganese, sometimes of oxide of iron. 
Their origin appears to resemble that of the flowers of ice 
on window panes, or the so-called silver trees. 

Slickenslides, Friction Surfaces (Germ. Tlutschflaclien, 
Reibungsjlaclien, Schliffflachen, Spiegelftachen, or Har- 
nische). The surfaces of solid rocks are sometimes found 
to have been naturally smoothed or polished, and also 
furrowed or scratched in some one direction. This phe- 
nomenon occurs in the most various kinds of rocks, some- 
times in the interior of the earth, sometimes on the exposed 
surface of the rock. When it occurs in the interior of 
the earth, it has been invariably caused by masses of rock 
pushing and shoving against each other, and forms one of 
the clearest proofs of such movements having taken place 
in the solid crust of the earth. Friction surfaces when 
met with on the exposed face of a rock may no doubt 
have been likewise caused in the same manner, and have 
been laid bare subsequently, but in fact they have very 
often been caused by the progressive movement of a glacier 
rubbing over the surface of the rock. These latter friction 
surfaces may be distinguished from the former kind by 
the uniform direction of their furrows, always correspond- 
ing to the indications of the valley, and further by their 
never exhibiting protuberant masses between the furrows, 
as is sometimes the case with the others. They are to 
be met with in districts where glaciers once existed. 
Floating ice is said sometimes to produce similar marks on 
rocky sea-coasts. 



EXTERNAL STRUCTURE. 101 

Many hard rock surfaces exhibit a peculiar smoothness 
with at the same time a wavy conformation or a furrow- 
ing in one particular direction. It has been observed 
that sand set in motion by the wind and driven against 
the surfaces of rocks for very long periods of time, has 
produced the like singular abrasions. This phenomenon, 
first described by Naumann (who ascribed it to glacial 
action), is observable in certain rocks at Wurzen, in 
Saxony. (See v. L. und B. Jahrb. 1844, pp. 557, 561, 
680; 1848, p. 497.) 

It is familiar to every one how running water will 
gradually round off and eat into the hardest rocks. 
The singular phenomenon of what are called pot-holes 
or ^iant-holes deserve special mention. These circular 
hollows are formed at waterfalls or rapids by whirl- 
pools carrying sand or pebbles round and round, and so 
gradually scooping out a smooth round hollow. Basins 
of this kind are found in river beds from a few inches to 
many feet in diameter, and even over the height of a man 
in depth. In places where the origin of these basins is 
not to be explained by any existing waterfall or stream, 
we must presume the former existence of such. 

Somewhat analogous to the pot holes are the so-called 
f Karren* or ' Karrenf elder] which are terms of Swiss 
geologists for certain rill marks hitherto only observed on 
limestone and dolomite rocks. They usually only occur 
in lofty mountain districts, and are very frequent in the 
Alps. They consist of gutters of from a quarter of an 
inch to two feet wide, washed out of the face of the rock 
by the rain, and following the lines of its steepest in- 
clination. 

Rocks locally possessing different degrees of hardness 
when exposed to the weather and the action of rain often 
present a singular jagged, glandular, or honeycombed 
appearance from the unequal degree of resistance of their 
parts. Thus, for instance, the quadersandstone of the 
Saxon Switzerland, the argillaceous gypsum of the Kiff- 
hauser, &c. 

The traces of raindrops are not unfrequently found on 
rock surfaces. These raindrops must have fallen during 
the formation of the stratum, probably at ebb tide, mak- 
ing small holes surrounded with raised rings. These 



102 PHYSICAL STRUCTURE OF ROCKS. 

holes have then been covered by the next stratum, and so 
preserved for all time, like the ripple- and current-marks, 
which are also of frequent occurrence on the surfaces of 
some sedimentary rocks. Vide Froriep's Neue Notizen, 
1839, vol. xi. p. 134 ; Ann. d. Sc. geol. 1843, p. 61 ; 
Compt. rend. 1861, vol. 53, p. 649; Lyell in Koyal 
Institution of Great Britain, 1851-4, Cepr. und Geologic 
(translated 1858), i. p. 390 ; i. p. 150. 

Animals also take part in the transformation of rock 
surfaces. Certain kinds of mollusca on the sea coast 
(Pholades) have the peculiar habit of burrowing several 
inches deep into limestones or dolomite rocks, and even 
into clays as well as much harder rocks ; (as, for instance, 
mica-schist), so as by degrees to perforate the whole 
surface. Ancient lines of coast are sometimes to be re- 
cognised by means of their appearance. 

Rounded Stones, Gravel) Shingle, Pebbles, or Boulders. 
These stones have usually been wholly or partially 
rounded by the action of water. There are, however, 
such as have been rounded by the motion of glaciers, and 
some even appear to have been rounded in clefts of 
rocks, the sides of which have been much agitated. 

There are also some special points respecting them 
which deserve attention. In the first place most pebbles 
are not spherical, but flattened and lenticular or elon- 
gated, egg-shaped, &c. This very universal law is evi- 
dently the result of an unequal degree of resistance to 
waste presented by the stone in the direction of one or 
more normal axes. In the case of rocks of slaty texture 
or the like, this phenomenon may be readily conceived ; 
but in the case of compact or granular rocks without a 
trace of fissile or laminated texture, it is more remarkable, 
and points to some parallelism of texture or structure 
which has hitherto escaped observation. 

The boulders or pebbles formed by glaciers sometimes 
exhibit grooves or scratches on their surface. 

At the foot of the Alps in the neighbourhood of Vienna, 
many pebbles and boulders have been formed showing 
deep grooves and forcible impressions, and some which 
are partially broken and pieced together again. 

In some conglomerates (as in the Nagelflue of St. Gall) 
pebbles are found partly forced into each other (these are 



EXTERNAL STRUCTURE. JOINTED STRUCTURE. 103 

usually of limestone), and in other conglomerates, for in- 
tance at Waldenburg in Silesia, there are pebbles which 
have been cleft asunder, their several parts somewhat dis- 
placed, and so cemented together again. But perhaps the 
most remarkable of these phenomena are the dolomitic 
limestone pebbles in a conglomerate at St Lauretta in 
the Leitha mountains, many of which are hollow. 

Much has been written on these peculiar forms and 
phenomena, as appearing in pebbles. We have referred 
to the greater part of such treatises in a former work 
(vide Geolog. Fragen, 1858, pp. 198212), and will only 
here add a reference to some later treatises, viz. : 

WUrttmlerflcr in von L. & Br. Jahrb. 1859, p. 153. 
Deicke, ibid. 18(30, p. 219. 

(.'nrlt, ibid. 1861, p. 225. 
Serggeist, 1860, p. 382. 

Sorby, On the Direct Correlation of Mechanical and Chemical 
Forces. 

JOINTED STRUCTURE. 

All large masses of rock are internally cleft by fis- 
sures or joints, and thereby divided into solids of different 
size and form. The general cause of this jointed structure 
of the mass is evidently contraction which, in the case of 
the igneous rocks, in all probability took place during 
cooling ; in the case of the sedimentary during the process 
of their drying; and in the case of the metamorphic, which 
they inherited from the sedimentary, or which was re- 
newed during the process of metamorphism. 

In most rocks the jointing is irregular, dividing the 
rock into irregular masses ; frequently, however, a cer- 
tain degree of regularity is exhibited i.e. the dividing 
fissures observe one or more prevailing directions, and are 
at definite distances from each other, so as to form a 
severance into tolerably regular plates, columns, paral- 
lelopipeds, or spherical masses. 

This so-called jointed structure deserves to be here 
described with some particularity, although it has no 
connection with the mineralogical composition of the rock, 
and solely results from the circumstances attending its 
original formation, and especially its solidification. 

Tabular Jointing. The rock's mass is split into parallel 
plates or tables, and these, unlike flagstones or strata, 



104 PHYSICAL STRUCTURE OF ROCKS. 

have not been successively deposited one over the other, 
but were all formed simultaneously and subsequently to 
the first formation of the rock. This constitutes, indeed, 
the characteristic distinction between stratification and 
jointing the former being the result of successive super- 
position, the latter of the splitting of a previously formed 
mass. Tabular jointing occurs most frequently in the 
igneous rocks, less frequently also in the sedimentary 
and metamorphic. 

A modification of the tabular structure sometimes 
occurs, consisting in a curvature of the individual plates, 
which are frequently very thin. This is called in German 
Schalige absonderung, ' conchoidal jointing.' 

Columnar, Subcolumnar, Prismatic Jointing. The 
rock's mass is split into columns of from 3 to 9 faces, 
usually 5 or 6 faces, and the thickness of the pillars in 
each place is tolerably uniform, but in different places 
varies from a few inches to several feet. The length of 
the columns is of course unequal. Some are known more 
than 200 feet long. These columns are, however, usually 
cross-jointed i.e. split into shorter blocks by means of 
cross courses or horizontal fissures at right angles with 
the first set of joints. This jointing is regular or irre- 
gular, it sometimes exhibits rounded surfaces, indicating 
in that case that the pillars were formed by the joining 
together of spherical masses (as may be clearly seen, 
indeed, in some places). 

Columnar jointing may be observed with peculiar fre- 
quency and beauty in basalt, but it also occurs in diabase, 
diorite, aphanite, and quartz-porphyry ; less frequently in 
trachyte, granite, or syenite. In all these rocks this 
jointing is evidently the result of a special process of 
cooling ; moreover, the axes of the columns are for the 
most part at right angles with the plane of the larger 
cooling surface. In lava streams, for instance, perpen- 
dicular to their surface ; in veins or dykes of basalt, per- 
pendicular to the walls of the cleft. If the larger cooling 
surface has been curviform, the columns at right angles 
to it will be found bent or radiating. 

But sedimentary rocks sometimes exhibit the pheno- 
menon of columnar jointing. In them it is probably owing 
to having dried more rapidly from one side of the mass, 



JOINTED STRUCTURE. STRATIFICATION. 105 

and in rare cases, locally, to the effect of heat from con- 
tact with igneous rocks. 

Parallelopipedic, Cuboidal, or Rhomloidal Jointing. 
The rocks are severed by joints which traverse them in 
planes of three different directions, which, if they cross 
each other at right angles, produce cubes or rectangular 
parallelepipeds ; if at inclined angles, rhomboidal solids. 
In sedimentary rocks the direction of one of these planes 
is frequently determined by the bedding, but in igneous 
rocks all three sets of joints are independent of such 
influence. 

Spherical, Globular, or Spheroidal Jointing. Some 
rocks are entirely composed of spherical masses, the in- 
terstices or spaces originally existing between them being 
now filled with a mass of similar substance and compo- 
sition, but so that the jointing is still apparent. These 
spherical masses are often formed of concentric layers, 
and sometimes ranged over each other in columns. In 
the latter case the globular and columnar jointing may be 
said to be combined. 

A modification of the spherical structure is what is 
called ball and socket jointing, in which single masses 
with rounded heads more or less approach the globular 
shape, and seem to fit into a cavity on the other side of the 
fissure. 

This passes over into irregular or massive jointing, 
which occurs more or less distinctly in rocks of the most 
different description. 

All jointing becomes much more distinctly apparent 
when the rock is weathered, and it sometimes even ap- 
pears as if the structure were solely caused by decay of 
the rock. Nevertheless, it is very probable that even 
in these cases a disposition to the severance previously 
existed. 

STRATIFICATION OF ROCKS. 

We have already spoken of the lamination of shaly 
rocks as consisting of a structure dividing those rocks in 
planes parallel to their bedding, and originating in the 
mode in which they were formed i. e. by successive 
layers of deposit. 



106 PHYSICAL STRUCTUKE OF ROCKS. 

The same phenomenon on a larger scale is called strati- 
Jication, and the individual members of the series are 
termed strata. Page observes in his Adv. Text Book, 
6 Thus ' (speaking of stratified rocks), ' the terms stratum 
and bed are used when the deposit is of considerable 
thickness ; layer or band when it is thin, and holds a 
subordinate place among the other beds ; and seam when 
a rock of a peculiar character occurs at intervals among 
a series of strata. The miner, for example, speaks of a 
seam of coal occurring among strata of clay and sand- 
stone, and of a band of ironstone occurring in a bed of 
shale.' 

The horizontal line on the surface of strata is termed 
the strike, and their steepest inclination towards the hori- 
zontal plane is termed the dip. 

Stratification is exhibited more especially and distinctly 
in the sedimentary rocks, but it is also frequently to be 
recognised in the metamorphic, and even the igneous rocks 
may exceptionally be actually stratified, if, for instance, 
successive streams of lava have overflowed each other, 
each consolidating separately. 

SHAPE AND BEDDING* OF EOCK MASSES. 

Both the shape and the mode of bedding of rock masses 
are dependent on the mode of their original formation. 

Igneous rocks neither exhibit any certain shapes nor 
any uniform bedding in relation to other rocks, whereas 
in the case of sedimentary rocks and their offspring, the 
metamorphic, both shape and bedding have some relation 
to certain general laws. 

The form assumed by igneous rocks depends to some 
extent on the shape and size of the opening by which 
they forced their passage from the interior of the earth. 
They accordingly fill clefts more or less regular in form, 

* The word ' BEDDING ' is used indifferently throughout this work 
in speaking of all rocks, whether stratified or not. It is taken as the 
equivalent of the German ' Lagenmg? We are aware that in England 
this has not been always usual ; nevertheless, some general word must 
be adopted. f Mode of occurrence/ ' position/ 'lie,' &c., are all ex- 
pressions which fall short of the idea intended to be conveyed. 
TKASTSLATOK. 



SHAPE AND BEDDIXG OF ROCK MASSES. 107 

or they occupy larger irregular spaces between other 
rocks, or they have overflowed through craters, and create 
accumulations after the manner of lava in streams, in 
plains, or conical heaps. 

Where the igneous rock forms a clear and evident 
filling of a previously existing cleft or fissure, it is termed 
a dyke or vein. The latter term is, however, more usually 
confined by many to such as are metalliferous. The irre- 
gular disrupting masses are called in German Stb'cke (ste- 
hende or liegende Stocke), for which terms there are no 
precise equivalents in English nomenclature of very 
general acceptation. Where igneous rocks are accu- 
mulated in great extent, and they appear to have filled 
greater gaps in the earth's* crust, they are spoken of as 
ranges, districts, or tracts. These are sometimes of ap- 
proximately circular or elliptical shape in their horizontal 
extension, as may be observed on geological maps. From 
such ranges, again, there frequently run smaller branches 
in different directions (ramifications). 

W'here igneous rocks in a state of fusion have broken 
through other rocks and spread themselves over the latter, 
they are said to be overlying. They are either extended 
longitudinally in one direction in the manner of streams 
of lava, or they cover broad surfaces, and form extensive 
fields. In both cases they may afterwards be themselves 
covered by later rock formations. 

The form which the igneous rocks assume above the 
surface of the ground corresponds little with that of their 
mass beneath, the geographical outline alone is determined 
by the latter not the elevation. Very recent igneous 
rocks, by reason of their volcanic origin, may be of coni- 
cal shape, as is the case with many basalts, phonolites, or 
trachytes ; but all the older igneous rocks owe their pre- 
sent shape to the transforming influence of long continued 
weathering and flooding, so that their present appearance 
depends much more on their individual power of re- 
sistance to those influences than upon the shape in which 
they first made their appearance on the surface of the 
globe. 

The shape of the sedimentary and metamorphic rocks 
is always flat, or nearly so. Their material was originally 
deposited on surfaces more or less even, and if inequalities 



108 PHYSICAL STRUCTURE OF ROCKS. 

existed they were filled up, so that at least the upper 
strata of such deposits are always very regularly flat 
shaped, or very broadly lenticular. The general shape 
and extent of these rocks corresponds therefore, more or 
less, with that of every individual stratum of the same. 
The conformation of the actual surface in many cases has, 
however, been much changed by external forces, such as 
weathering, the action of flood waters, &c. ; and, again, the 
lowest beds of the series may exhibit very great inequal- 
ities ; even former rents or fissures in underlying rocks 
may have been filled up by the material of the deposit, so 
that these fillings of clefts may subsequently assume the 
shape and character of veins or dykes, in the underlying 
rock. Such last mentioned cases, however, are rare. 

Rents in the earth's crust have come to be filled in very 
various ways, e. g. by the injection of matter in a state of 
igneous fusion, by mechanical deposit from above, or by 
chemical precipitate from solutions. Such fillings are 
called dykes, veins, or lodes. The term lode is exclusively 
applied to a metalliferous vein ; so also by some geologists 
is the term vein, but this is not the universal practice. 
The term dyke is exclusively applied to such as consist of 
the same material throughout. 

Although the sedimentary rocks, as a rule, form exten- 
sive flat-lying systems of stratification, yet there occa- 
sionally occur irregular accumulations distinguished from 
the ordinary flat strata by proportionately greater thick- 
ness and less horizontal extent, as well as by irregularity 
of shape. They may have sometimes arisen by filling of 
caverns. 

The bedding of rocks may be divided into the regular 
and irregular. The latter is characteristic of the igneous 
rocks, the former of the sedimentary and metamorpnic. 

Irregular bedding is in general the consequence of a 
violent disruption of the pre-consolidated earth's crust. 
The igneous rocks have forced themselves a path through 
the existing rocks and filled up the cracks made in the 
latter by the eruption. These are sometimes, but not 
always, regularly formed fissures, such as when filled can 
be called dykes. These violent disruptions are termed 
intrusions, and when they are of unmistakable character 
we may conclude with certainty that the intruding rock is 



SHAPE AXD BEDDING OP ROCK MASSES. 109 

of more recent formation than the one broken through, 
but not how much more recent. 

Regular Bedding, which, as we have said, chiefly pre- 
vails in the sedimentary and metamorphic rocks, corre- 
sponds with their internal stratification. 

The following are some of the phases of bedding : 

1. Parallel alternating bedding, or uniform bedding, when 

two or more rocks alternate with each other in 
parallel strata, forming a whole system of strata 
whose general shape is flat or gently swelling. 

2. Divergent bedding. When any set of beds incline in 

different directions, they sometimes incline towards 
each other (synclindt), and sometimes they fall 
away from each other (anticlinal). 

3. Overlapping (ubergreifend), when one set of strata 

overlaps the edges of another set of strata. 

4. A hollow basin-like form (Muldenformig). 

5. Cloak-like bedding (Mantelformig), where the strata 

or beds surround and nearly envelop a central 
point from which they dip on all sides (quaqua- 
versal dip). 

6. Subordinate intermediate bedding, when beds of subor- 

dinate size lie in the midst of a larger series of 

strata. 

The originally regular bedding of the sedimentary and 
metamorphic rocks has very often been more or less dis- 
turbed by subsequent processes, such as the intrusion of 
igneous rocks, subsidence, &c., and even some of the 
above-named cases are sometimes only the consequence of 
some such disturbances. The natural or original position 
of the sedimentary or the metamorphic rocks and their 
strata is necessarily the horizontal, or nearly so. If we 
find any very great variations from the horizontal, these 
are, as a rule, to be considered as the consequence of dis- 
turbance, although the original cause of such disturbance 
may not always be recognised with certainty. 

The following are some of the different kinds of dis- 
turbance of bedding: 

1. Uplifting, by which whole strata or systems of strata 

frequently appear to have been very strongly in- 
clined from the horizontal direction. 

2. Contortion, foldings, bendings. 



110 PHYSICAL STEUCTURE OF ROCKS. 

3. Disruption, breaks (Zerknickung), where the strata 

appear to have been uplifted in the centre and 
broken, the two parts dipping from the place of 
rupture. 

4. Displacement or faults (Yerwerfung) where one por- 

tion of the bed has been uplifted or depressed and 
bodily separated from the remaining portion. 

5. Subversion (Ueberstiirzung), where the bed has been 

entirely overturned, and its position reversed. 
From the bedding of rocks we may often, but not 
always, determine their relative age. The principles to 
guide us in this are somewhat as follows : 

1. Overlying rocks as a rule are more recent than those 

which they cover. 

The only exceptions to this rule are created by 
subversions, or by obliquely upheaved or intruded 
igneous masses. Such exceptions, however, are 
usually easily to be recognised by surrounding 
circumstances. 

2. Intruding rocks are always more recent than those 

which they have penetrated. 

The exceptions to this rule can be only apparent ; 
as for instance, if a steep projecting rock has been 
surrounded by and come to be imbedded in a later 
deposit and so afterwards possibly been mistaken 
for an intruder. 

3. Rocks which during their formation have created 

manifest disturbance of the bedding of other rocks 
are necessarily in every case younger than those. 

From this rule also only apparent exceptions 
can arise, as when the bedding of a rock may have 
been disturbed by the decay of the underlying 
stratum, e. g. the dissolution of rock-salt. 

4. The level of a rock alone will not enable us to pro- 

nounce on its age, for the oldest sedimentary rocks 
may by upheaval have been shoved up into the 
highest level ; and as regards the igneous rocks, 
according to their very nature the oldest and the 
youngest may be met with in any level. 



Ill 



CHAPTER IV. 

GEOLOGICAL FORMATIONS AND GROUPS OF ROCKS. 

ACCORDING to the present state of our geological know- 
ledge, we regard a certain class of rocks as the original 
products of the consolidation of parts of the fused mass of 
which our planet formerly consisted, and which we still 
believe to be the substance of the interior of the globe. 
These original products we term igneous rocks. All other 
rocks are only secondary products arising from their 
transmutation, their decomposition, decay or -disintegra- 
tion, and reconstruction. 

The igneous rocks are subdivided into two principal 
groups, the Volcanic and the Plutonic. The volcanic are 
those which, having been ejected from the interior in a 
fluid or viscous state, cooled and consolidated at or near 
the surface of the earth. The plutonic are those rocks 
which have not reached the surface of the earth in a fluid 
or viscous state, but solidified at considerable depth, 
probably therefore under influences of great heat and 
pressure. 

The rocks which we have termed secondary products 
are likewise divisible into two great classes, the Sedi- 
mentary and Metamorphic. The sedimentary rocks being 
formed from the debris of the igneous rocks, and the 
metamorphic being the older sedimentary rocks, which, in 
process of time, and from various causes, have assumed an 
altered character, have undergone ' metamorphosis.' Let 
us take a brief review of these principal rock forma- 
tions : 

1. Volcanic Formations. The active volcanoes of the 
present day furnish us with the best instances of 
these formations, and the surest data for consider- 
ing the phenomena of their origin. First we find 
consolidated lavas of various outward form and 



112 GEOLOGICAL FORMATIONS 

internal structure ; they assume the shape of narrow 
streams down the mountain side, they overflow the 
plains in broad sheets, or filling up previously 
existing cracks and fissures they form veins or 
dykes in other rocks, or they form conical mounds 
on the mountain top. The column of lava which 
solidifies in the abyss of the crater must frequently 
assume the shape of a vertical cylinder, Avhich, 
however, remains inaccessible to observation, unless 
and until a considerable portion of the whole moun- 
tain has decayed and been washed away. 

The lavas consist either of basaltic or trachytic 
rock ; their inferior mass is either compact, por- 
phyritic, or crystalline-granular, their exterior 
frequently vesicular or scoriaceous. 

Thus there are many different rocks or varieties 
entitled to be called lava, and all belonging to one 
and .the same formation. Besides the lavas proper 
we find at volcanoes various kinds of loose ejected 
masses, some more and others less decomposed, 
consisting of large concretions of slag, smaller 
fragments of lava (lapilli), volcanic sand, and dust- 
like particles, so-called ' volcanic ash.' These 
ejectamenta either remain lying loose on the sur- 
face of the ground, or they form conical piles K of 
slag, or they are washed together by water and are 
redeposited as volcanic tufa, which thus may be of 
very various character. 

2. The older Volcanic Formations differ from the most 
recent by the entire or almost entire absence of 
loose ejectamenta, scoria, evident streams of lava, 
and distinct craters. No doubt all these were once 
in existence, but in course of time they have de- 
cayed and been washed away. We now only find 
bare conical hills of basalt, dolerite, trachyte, or 
phonolite (the kernels which have remained of 
former volcanoes after the decay of the masses which 
surrounded and covered them), accompanied by 
veins branching out of those nucleous masses, and 
by tufa formations or other decomposed forms of 
volcanic product. So much of the outer vesicular 
or scorified coating of the original volcanic rocks 



AND GROUPS OF ROCKS. 113 

as has not been entirely destroyed and washed 
away has in the course of time been turned to 
amygdaloid. These older volcanic formations, like 
the more recent, are partly basaltic and partly 
trachytic, and they form transition states between 
the volcanic and plutonic formations. 
3. Upper Plutonic Formations. These may be divided 
into such as are of prevailing basic and acidic com- 
position, characterised respectively by the green- 
stones and quartz-porphyries. The Voigtland in 
Germany presents us with a good example of 
the basic greenstones, and the north-western dis- 
trict of the Thuringian Forest of the acidic quartz- 
porphyries. 

In the Voigtland, associated with transition rocks, 
we find various kinds of greenstone, such as diabase 
andaphanite, granular, compact, porphyritic, fissile, 
and amygdaloidal, some decayed into wacke, some 
in the form of tufa, or conglomerate. These green- 
stones, it would appear, constitute the subterranean 
portion of a volcanic formation of the Devonian 
age. We must assume that the upper and perhaps 
more basaltic portion of this formation has decayed 
away; loose ejectamenta and genuine volcanic 
shapes are no longer observable ; the conical hills 
of greenstone are doubtless the result of the supe- 
rior power of resistance of that rock, just as quartz 
rocks frequently protrude above masses of a softer 
rock which formerly enclosed them. It is, never- 
theless, remarkable that the tufa and conglomerates 
which have been preserved imbedded in the tran- 
sition strata appear to have been originally green- 
stone and not basalt, whence we might conclude 
that even the original volcanic portion of these 
eruptive formations which reached the surface 
rather resembled greenstone than basalt. 

In the Thuringian Forest quartz-porphyries 
predominate ; they are of various kinds, and are 
associated with mica-porphyrites and greenstones, 
claystone tufas and conglomerates. The conglo- 
merates contain fragments of rocks belonging 
unmistakably to the Rothliegende or Dyassic age, 



114 GEOLOGICAL FORMATIONS 

so that we must conclude that the eruptions which 
upheaved these Thuringian porphyries took place 
during that period or subsequent to it. Every 
trace of genuine volcanic formation has long since 
decayed and been swept away ; the plutonic part 
alone has remained, except, indeed, some tufas 
which have been preserved by superincumbent 
strata. It need hardly be said that the process of 
laying bare rocks which lay so deep must have 
occupied long spaces of time, and therefore plutonic 
rocks must be very old before they are exposed 
and rendered accessible to our observation. 
4. Lower Plutonic Formations. The most characteristic 
and strongly marked representatives of these for- 
mations are the granites (and syenites). These 
have consolidated in the earth at great depth. 
They are for the most part very distinctly crystal- 
line, though their texture is very various. 

They are never vesicular, nor do they occur in 
the form of tufas, for the latter could not possibly be 
formed in the interior of the earth. On the other 
hand, they are sometimes accompanied by friction 
breccias. They branch out into veins traversing 
other rocks as well as the older masses of the same 
formation. These branches have frequently cooled 
more rapidly than the general mass and formed 
themselves into porphyry. This result has been 
especially observed where the veins are narrow ; 
but the width of the veins has not been the only 
determining cause of more rapid cooling ; the depth, 
the temperature of the neighbouring rock, its state 
of moisture or dryness, must all have operated in 
hastening or retarding the consolidation of the in- 
truding mass. 

Tracts of granite frequently form the back-bone 
or nucleus of mountain ranges. They occur in 
larger masses and of more connected range than the 
upper plutonic formations. It would appear to be the 
case, as we might a priori have supposed, that upon 
the occasion of every eruption of igneous fluid 
from the earth's interior the opening made is wider 
below than at the surface. The eruptive mass 
when cooled acquires different characters according 



AND GROUPS OF ROCKS. 115 

to the pressure to which it has been subjected 
during the cooling process ; in other words, ac- 
cording to the depth at which it consolidated. The 
same eruptive mass may be volcanic at the surface, 
and plutonic below the surface of the earth. The 
plutonic rocks, in all probability, represent the 
upper portion of a conical mass, widening towards 
its base. Thus we may explain the fact that the 
lower plutonic rocks, when laid bare, occupy a 
wider area than the upper. It also follows that as 
a longer time would be requisite for their exposure, 
the lower plutonic rocks which are exposed to our 
observation are universally the oldest igneous for- 
mations for the time being ; and thus the granites, 
being those of the plutonic rocks which have con- 
solidated at the greatest depths, are for the most 
part the oldest of the igneous rocks of the present 
geological period. This does not however exclude 
the possibility of newer granite formations being 
accidentally exposed in some cases, for instance, by 
very violent local upheavings, or very rapid waste 
of superincumbent rocks, favoured by numerous 
fissures. This, in the Alps, has actually taken 
place. So much of the granite formations as 
reached the surface at the time of the eruption 
may perhaps have been of trachytic character, and 
it may be that the same masses which form the 
trachyte-lavas of the present time are simulta- 
neously forming granite rocks at great depths below 
the surface. The fact of the chemical composition 
of the two rocks being the same is at all events in 
harmony with such an hypothesis. 

These examples may suffice for the igneous rocks. TV r e 
next proceed to notice the chief sedimentary formations. 
(The metamorphic rocks being the products of the sedi- 
mentary, are consequently later in date of their formation 
than those.) 

5. Argillaceous Formations. These are deposits of clayey 
mud alternated with marl, lime, or sand, some- 
times containing a large proportion of hydrated 
oxide of iron. These deposits were, in process of 
time, covered by more recent strata, and produced 

I 2 



116 GEOLOGICAL FORMATIONS 

clay-slate, argillaceous shale, interstratified with 
calcareous shale, compact limestone, sandstone, 
and ironstone. Such formations have taken place 
in all geological periods. 

6. Marl Formations. These deposits consisted chiefly 

of marly silt alternating with clay, calcareous mud, 
sand, and sometimes gypsum or hydrated oxide of 
iron. Under the pressure of superimposed strata, 
these deposits became converted into marl-shale 
and compact marl, interlaid with strata of argil- 
laceous shale, limestone, gypsum, and ironstone. 
A very characteristic marl formation of this nature 
is met with in the German keuper. 

7. Limestone Formations. These are the result of the de- 

posit of calcareous silt, invisibly small shells, larger 
shells, coral reefs (partly dolomitic) or calcareous 
tufa, alternating with calcareous, argillaceous, or 
sometimes siliceous strata. From these under the 
pressure of superjacent formations, there have re- 
sulted beds of limestone and dolomite of many dif- 
ferent varieties, earthy and compact, in alternate 
strata with subordinate beds of marl-shale, clay- 
slate, argillaceous- shale, ironstone, or flint. In 
every geological period these deposits have taken 
place ; we find them very characteristically de- 
veloped in Germany in the Jurassic, Muschelkalk, 
and Zechstein formations. 

8. Sandstone Formations. These are deposits of quartz 

sand (more or less fine-grained) with some clay 
marl or protoxide of iron. Pebbles also have been 
deposited with the sand either locally interspersed 
or in alternate beds. The deposited sand when 
subjected to pressure then became sandstone, and 
the other ingredients formed themselves into in- 
termediate strata of slate-clay, marl-shale, conglo- 
merate, and the like. These formations have taken 
place in all geological periods. Very characteristic 
instances are furnished by the Quader-sandstone 
and variegated sandstone (Buntsandstein) of Ger- 
many. 

9. Conglomerate Formations. The original deposits were 

chiefly pebbles, sand, and clay. From these materials 






AND GROUPS OF ROCKS. 117 



by pressure, solid conglomerates were formed, con- 
sisting of pebbles cemented together by the sand 
or clay, and inter stratified with beds of sand or 
clay. These deposits have taken place in all 
periods, but have never attained any great extent 
at one time or place. Hence the conglomerates 
play a very subordinate part in the sedimentary 
formations. In Germany, there is properly speak- 
ing but one very characteristic conglomerate for- 
mation, which is that of the Rothliegende. The 
Nagelflue of the Molasse formation is quite subor- 
dinate to the sandstone, which is the predominant 
rock of that formation. 

10. Coal Formations. The greater part of these forma- 

tions originally consisted of peat, or vegetable 
materials washed together ; usually sand and clay 
were likewise contained in the deposit, and some- 
times hydrated oxide of iron or protocarbonate of 
iron. These deposits, in the course of time, with 
pressure, were formed into strata of alternate sand- 
stone (usually grey) and slate-clay or shale ; and 
between these strata, beds of brown or black coal 
or anthracite and clay-ironstone were formed, sub- 
ordinate, however, in extent and thickness to the 
sandstone, slate, and shale. Coarse conglomerates, 
marl, or limestones very rarely occur in these for- 
mations. 

The Carboniferous period and the Tertiary period 
furnish the most characteristic examples of these 
formations ; but the carbonaceous deposits of other 
periods are associated with similar rocks, and are 
so like the genuine coal formations that, petro- 
graphically, they are hardly to be distinguished 
from them. 

11. Rock-salt Formations. Rock-salt is always accom- 

panied by gypsum and anhydrite, and it likewise 
usually occurs in combination with argillaceous 
deposits. The rocks of this group are usually 
imbedded in limestone or dolomite, as in the 
Muschelkalk of Germany, or in sandstone as in 
Galicia and Transylvania. In all periods these 
local deposits appear to have taken place* but 



118 GEOLOGICAL FORMATIONS 

the special conditions and causes of their origin 
are not yet known with certainty. 

If we turn to the rocks which we consider 1o be of 
metamorphic origin, the crystalline schists, we find alter- 
nating beds analogous to those of the sedimentary rocks, 
but in an altered state. We, kowever, seldom or never 
find rock-salt or gypsum, a circumstance which may be 
explained by the great solubility of those rocks. 

The crystalline schist formations may be best described 
by naming the principal rocks of each. Thus we have : 

12. Argillaceous Mica-schist Formations, with subordinate 

beds of quartz-schist, lydian stone, alum-schist, 
granular limestone and dolomite, sometimes also 
hornblende-schist, ironstone, and graphite. 

13. Mica-schist Formations, with similar subordinate for- 

mations to those in the argillaceous mica-schist. 
In these we include some kinds of gneiss. 

14. Gneiss Formations, consisting of gneiss of various 

kinds in parallel and alternating strata, and con- 
taining similar subordinate formations to the mica- 
schists. 

15. Chlorite-schist Formations, also containing similar 

subordinate beds of other rocks. 

These formations seem to be the result of a 
special process of transmutation occasioned by the 
presence of magnesia. 

The fact that in the crystalline schists coal, gypsum and 
anhydrite are much more rarely met with than in the sedi- 
mentary formations, and rock-salt almost never, may, as 
we have already said, be accounted for by the perishable 
nature of those rocks. It seems remarkable that con- 
glomerates are also very rarely met with. We should 
not, however, forget that these only play a subordinate 
part in the sedimentary formations, where they are 
usually only of local occurrence. They are, moreover, 
found in some crystalline schists, as, for instance, in 
Valorsino and in the Upper Rhine Valley, in the west 
Alpine district, where they occur in the gneiss and mica- 
schist formations, and pass over by transition into those 
rocks, their cementing medium having become crystalline, 
and the pebbles blended with the general mass. 



AND GROUPS OF ROCKS. 119 

The following is a list of the great geological periods 
of deposit: 

POST-TERTIARY EPOCH : 
Recent period (human). 
Pleistocene period. 

TERTIARY EPOCH : 
Pleiocene period. 
Meiocene period. 
Eocene period. 

SECONDARY or MESOZOIC EPOCH : 
Cretaceous period. 
Oolitic period. 
Triassic period. 

PRIMARY or PALEOZOIC EPOCH : 
Permian period. (Dyas.) 
Carboniferous period. 
Devonian period. 

Silurian period (upper and lower). 
Cambrian period. 
Pra3-cambrian periods. 



120 TRANSITIONS AND TRANSMUTATIONS. 



CHAPTER V. 

TRANSITIONS AND TRANSMUTATIONS. 

WE have hitherto treated generally of the composition 
of rocks, their texture, and other outward characteristics, 
and their formation or origin. It is comparatively easy 
to describe these phenomena in general terms, but their 
application to particular rocks in describing and classify- 
ing them is a task of great difficulty. One of the prin- 
cipal difficulties of classification is occasioned by the great 
number of rocks of character varying more or less from 
the established types. These varieties, in many cases, 
form series with every shade of divergence from the 
normal rock until the last member of the series presents 
a totally different species, coinciding may be with some 
other normal type. A series of intermediate rocks thus 
connecting two established types is termed a series of 
transition ; and thus, in the abstract, one type is said to 
pass into the other ; not, however, that any real transition 
takes place of the actual rock, but merely, as we have 
said, that two groups are connected together by a chain of 
rocks partaking partly of the attributes of each. 

Transitions of this kind are met with in nature in 
almost all kinds of rock, in respect alike of their composi- 
tion, their texture, and their origin. A few instances will 
suffice for explanation. 

1. Transitions in respect of composition are said to take 
place when in a rock of given character a strange 
mineral ingredient occurs not usual in rocks of 
that class, or when an essential ingredient of its 
composition diminishes or altogether disappears. 

For instance, in the case of limestone and dolo- 
mite, a rock consisting essentially and principally 
of calc-spar (carbonate of lime) is a limestone, even 
though it contain some bitter spar or carbonate of 



TRANSITIONS AND TRANSMUTATIONS. 121 

magnesia ; but if enough of the latter enters into 
its composition, then the rock will be a dolomite ; 
and an endless variety of rocks are found with very 
different proportions of those two ingredients, so 
that it is impossible in many cases confidently to 
describe them either as limestone or dolomite. 
These are transition states between those two typi- 
cal rocks. Again, in the case of gneiss and mica- 
schist, we find first some, and then more felspar 
entering into the composition of a mica-schist, until 
at last we obtain a gneiss ; or we find less and less 
felspar in a gneiss, until at last it is reduced to a 
mica-schist. These and the like transitions may 
actually be observed in nature side by side, so that 
in the same mass we may sometimes find at one 
end a limestone, at the other a dolomite ; at one 
extremity a gneiss, at the other a mica-schist, &c. ; 
but the term transition is employed in this and 
other treatises in a wider sense to characterise any 
rocks of intermediate composition, wherever occur- 
ring, by means of which a relationship or connection 
may be traced between any two species of rock. 

2. The same kind of transition takes place between rocks 

in respect of their outward characteristics. The 
texture of rocks of every kind varies indefinitely 
from one type to another, without any sharp dis- 
tinction between the types; thus granite passes 
over into gneiss in numberless instances where it 
is more or less foliated in texture ; or granite-por- 
phyry passes into porphyritic granite by means of 
those rocks whose matrix partakes more of the 
granular than the compact texture ; or basalt into 
dolerite, by those varieties in which the individual 
minerals are somewhat more separately developed 
(granular) so as to be partially recognisable. 

3. Transitions occur between rocks in respect of their 

origin or mode of formation. Certain rocks are 
only the result of a transmutation of others, and 
the different stages of such transmutation have 
been distinguished by separate names. Thus 
argillaceous shale passes over into clay-slate and 
argillaceous mica-schist ; peat into browncoal ; 



122 TRANSITIONS AND TRANSMUTATIONS. 

browncoal into common coal ; common coal into 
anthracite ; and anthracite into graphite. Grabbro 
or granite passes over into serpentine. 

These last-mentioned transitions or transmu- 
tations are such in the strictest sense of the word, 
having been occasioned by changes of the rocks' 
substance in the course of time ; whereas the term 
transition, as applied to the two former classes is 
only a conventional term for a progressive series 
of rocks, all of which were from the first different 
from each other, and remain so. 

It need hardly be said that these several transitions 
and transmutations multiply not a little the difficulties of 
nomenclature and classification, and frequently render 
the desired precision and accuracy impossible. We are 
always driven back to this that every name applied to a 
rock can only be considered as establishing an especially 
characteristic form of its development as a kind of centre 
point, which, however, in nature is surrounded by nu- 
merous varieties and derivative forms of more or less 
doubtful character. 



123 



PART II. 

THE ROCKS. 



INTRODUCTORY CHAPTER. 

CLASSIFICATION. 

A SCIENTIFIC classification of rocks is a task of more 
difficulty than might at first sight appear ; as yet, no one 
has succeeded in producing a perfectly consistent and 
comprehensive system. Not only do the nature of the 
subject and our own imperfect knowledge present many 
serious obstacles to consistent arrangement ; but in many 
cases established usage and nomenclature, too firmly rooted 
to be lightly disturbed, prevent our changing an old classi- 
fication even when based on error. 

Even were our knowledge far more certain than it is, 
and were we free to overthrow all previous errors and 
misconceptions, we could not lay down a logically com- 
plete system of classification to embrace all rocks, on any 
principle, whether of ORIGIN, TEXTURE, or COMPOSITION 
(chemical or miner alogical). We do not find the minera- 
logical differences between rocks coincide with those of their 
chemical composition, nor are either of those dependent 
on geological position or stratification. There are no 
rigidly defined classes in nature. 

The student must not, therefore, expect too much from 
any system ; but, as we are driven to choose some basis for 
arrangement of our subject, we consider, on the whole, 
that the best scheme for our purpose will be one in its 
general features coinciding, as far as possible, with what 
we know of the origin of the various rocks, making use, 
however, of the distinctions arising from differences of 



124 CLASSIFICATION OF ROCKS. 

texture, composition, or otherwise, for the subdivision of 
our subject, as the nature of each case may seem to render 
advisable. 

A great number of distinctions have been established by 
custom between many rock formations, which in truth do 
not differ from each other very materially. These we shall 
as far as possible drop, endeavouring to make uniform 
connected groups, and treating many rocks, which have 
hitherto been known by different names, as varieties only 
of one and the same rock. On the same principle, we 
avoid as far as possible the introduction of new names for 
rocks. It is impossible, and would be unprofitable, to 
dignify every slight modification of texture or structure 
(perhaps only of local occurrence) by a separate name. 
Even in treating the most important and prevalent rocks, 
we should seek to confine our nomenclature to their most 
characteristic forms of development, establishing these as 
central points of departure, from which manifold transi- 
tions are found leading towards other central points in 
the next group of rocks. One observer may pronounce 
a doubtful rock to be granite, which another will call a 
gneiss, without our being able to say that one is right and 
the other wrong. In cases of this kind there constantly 
arises the temptation to give new names, but in the in- 
terest of science this temptation should be resisted as far 
as possible. 

The following are the general heads under which we 
have grouped the rocks in this work. 

I. IGNEOUS ROCKS* (Eruptive Rocks), all of which are 
most probably products of igneous fusion. 

* The term l IGNEOUS ROCKS ' is used throughout this book as the 
equivalent of the German l ERTJPTIV-GESTEINE. The Germans object 
to the term ' igneous/ as conveying the idea of fire or burning (which 
could not take place in the absence of air), and also because the meta- 
inorphic rocks may have been subjected to heat as well as those we 
call igneous. Most of our rocks have, however, been named in an im- 
perfect state of knowledge of their origin, and with reference to 
erroneous ideas; and if we are agreed on the signification of a term, 
we need not always go back to its derivation. Mr. Jukes objects to 
the German term ' eruptive] as applied indiscriminately to these rocks. 
He thinks that in speaking of the plutonic rocks, we should use the 
terms, ' irruptive ' or ' intrusive^ &c., as they did not, or are not sup- 
posed by us to have reached the surface at the time of their upheaval. 



CLASSIFICATION OF KOCKS. 1-25 

A. Rocks poor in silica, or basic rocks. 

(a) Volcanic. Of which the BASALTS are the principal 

representatives. 

(b) Plutonic. Of these the principal representatives are 

the so-called GREENSTONES (diabase, diorite, &c.). 

B. Rocks rich in silica, or acidic rocks. 

(a) Volcanic, e. g. the TRACHYTES. 

(b) Plutonic, e. g. the GRANITES. 

II. METAMORPHIC CRYSTALLINE SCHISTS. Most 
probably the product of the transmutation of sedimentary 
rocks, but in respect of their mineralogical composition 
closely allied to the igneous, e. g. GNEISS, MICA-SCHIST, 

CHLORITE-SCHIST, &C. 

III. SEDIMENTARY ROCKS. The products of deposit. 

1. Argillaceous rocks, such as CLAY and ARGILLACEOUS 

SHALE. 

2. Limestone rocks, such as LIMESTONE and DOLOMITE 

(including gypsum and anhydrite). 

3. Siliceous rocks, e.g. SANDSTONES and CONGLOME- 

RATES. 

4. Tufa formations. 

The above are the groups of principal rocks which 
occur in masses of great extent. 

IV. We shall next range those rocks of less frequent 
occurrence, or which only form subordinate strata or sepa- 
rate beds, and whose origin is in part still doubtful, without 
attempting in their case a logical classification. To this 
series belong, for instance, many silicates, the CARBONA- 
CEOUS ROCKS, the IRONSTONES, SERPENTINE, &C., and 
some other rocks of problematical character. 

V. Finally we shall instance those rocks which are 
essentially composed of one mineral, such as QUARTZ, 
OPAL, &c. 

The first book on rocks,, at that time a most masterly 
treatise, was von Leonhard's ' Charakteristik der Felsar- 

We have, however, kept to the term ' eruptive ' as a general term for 
describing the action of all igneous rocks ; and any other course would 
have compelled us to put a construction of our own on the origin of 
each rock, although not in the mind of our author, and unnecessary for 
his immediate purpose. TBAUSLATOB. 



126 CLASSIFICATION OF EOCKS. 

ten ' (1823). In it is to be found a reprint of Alexander 
Brongniart's * Classification mineralogique des roches 
melangees,' which had appeared in the 34th vol. of the 
Journal des Mines. 

The following are the most important among the more 
recent works on this subject : 

Naumanri's Geognosie, vol. i., a second edition of which ap- 
peared in 1858. 

Senffs Classification der Felsarten, 1857, in which the rocks 
are arranged with special reference to one or more charac- 
teristic ingredients. 

Durocher, Essai de Petrologie comparee in the Ann. des Mines, 
1857 ; ii. pp. 217 and 676. He separates the igneous rocks, 
in the same way that Bunsen did before him, into acidic 
and basic rocks. He subdivides these again according to the 
degrees of their acidity or basic composition ; these sub- 
divisions nearly correspond with Bunsen's l Mittelgesteine.' 

G. Bischof has examined and pronounced upon a large number 
of rocks from a chemical point of view. The arrangement 
of the separate treatises in his Lehrbuch der Geologie appears 
to be entirely accidental, and the geological relations of the 
rocks are hardly regarded.* 

Rammelsberg 1 s Handworterbuch der Mineralogie (with sup- 
plements) contains numerous analyses. 

Roth has recently attempted to collect all the known analyses 
of rocks and to arrange them according to fixed principles, 
accompanying them with critical remarks. 

Having referred the reader to the above-named compre- 
hensive works, we shall abstain from again quoting them 
in detail at the mention of each different rock. In dealing 
with the particular views of their several authors we shall 
only give the name of the author in question. 

On the other hand, we shall have occasion to cite at the 
proper places the valuable treatises of Abich, Biintsch, 
Bergemann, Blum, Breithaupt, Bunsen, Delesse, Deville, 
Ehrenberg, Fischer, Girard, von Hochstetter, Hochmuth, 
Jentsch, Knop, List, Nauriiann, Oppermann, vom Rath, 
Gr. Rose, Freiherr von Richthofen, Scheerer, Sochting, 
Stache, Streng, von Walterhausen, &c. 

* In the second edition (translated into English) there is much 
proyement in this respect. 



127 



CHAPTER I. 

IGNEOUS ROCKS. 

WHEN we consider the position and bedding of these 
rocks, and the disturbances and other changes they have 
effected in the strata and beds of other rocks, we cannot 
doubt that they have been forced upwards from the interior 
of the earth in a fluid or semi-fluid (viscous) state. They 
have penetrated and overflowed other formations and then 
become solid, partly in the clefts and partly on the surface 
of those rocks. The soft state in which they must have 
existed during their upheaval was in all probability the 
result of great heat, in other words, it was a state of 
igneous fusion ; hence the term Igneous Rocks. By pro- 
cess of cooling they then passed over into the solid state, 
assuming (under different circumstances) a crystalline- 
granular, a porphyritic, a compact or vitreous texture, 
sometimes vesicular, or sometimes even a fissile texture 
(schistose or slaty). Amygdaloids and wackes (as we 
have already seen) were of later origin, i. e. products of 
transmutation from original formations. 

As regards one great division of these rocks, their 
former state of fusion is capable of direct proof, and may 
be observed at the present day ; we see them in process 
of formation from the lava of active volcanoes. These 
are termed Volcanic Rocks. 

In the case of another class of those which we term 
Igneous Rocks, their former state of fusion is not so 
clearly evident ; indeed we occasionally find their com- 
position, their bedding, or their relative position with 
other formations in apparent contradiction to their assumed 
origin. It is supposed that these became solid at a con- 
siderable depth, some of them possibly having been poured 
out in a state of fusion like lava, but in the interior of 
the earth without reaching the surface, and consequently 
that their consolidation took place under very high pres- 



128 IGNEOUS EOCKS. 

sure, and more slowly than in the case of the volcanic 
rocks. They are therefore termed Plutonic rocks, and 
most geologists are agreed on the nature of their origin. 
The apparent contradictions to an igneous theory of their 
formation are to be explained by slow cooling, and the 
changes produced by time and high pressure. 

All igneous rocks consist principally of compounds of 
some kind of felspar (or leucite and nepheline) with 
pyroxene, hornblende, mica or quartz, generally also with 
some magnetic iron-ore and other subordinate minerals. 

We divide the igneous rocks, whether volcanic or plu- 
tonic, into those poor in silica (basic) and those rich in 
silica (acidic). 

The first class, the basic rocks, .are distinguished by 
their deficiency of quartz ; by their felspar being gene- 
rally poor in silica, and frequently richer in lime than 
that of the acidic rocks, and being mixed with pyroxene 
or hornblende ; by their texture being frequently vesicular 
or amygdaloidal, very seldom vitreous ; and by their ge- 
nerally prevailing dark colour. "^-. 

The acidic rocks on the other hand are distinguished 
by a felspar richer in silica ; by their frequently contain- 
ing a large proportion of quartz ; by their being rarely 
vesicular or amygdaloidal, but frequently vitreous ; and 
in general by their lighter colour. 

We might add that the basic rocks are more fre- 
quently compact and porphyritic than distinctly granular ; 
more frequently volcanic than plu tonic ; more frequently 
found in small unconnected masses than ranging in great 
tracts or regions ; whereas the acidic rocks on the contrary 
are more frequently distinctly granular and porphyritic 
than compact ; and more frequently extend over vast re- 
gions than occur in masses of very circumscribed extent. 
These data are, however, altogether general in their 
character, and must be taken with many qualifications. 

Bunsen was the first to draw attention to the scientific 
value of the difference between the basic and acidic 
rocks, which was previously little known, and had not 
been carefully investigated. He devoted himself to 
analysing rock-masses, and from the results of those 
analyses set up two normal types of composition (see 
page 364 post). We cannot, however, say that the com- 



COMPOSITION OF IGNEOUS ROCKS. 129 

position of the individual rocks of each of Bunsen's 
groups does more than approximately correspond with 
those normal values. In fact it would be more accurate 
to describe the individual values as fluctuating between 
two extremes than approaching any one central type. 
With this explanation we present the reader with our 
view of the composition of the two classes of rocks (the 
basic and acidic) differing somewhat, but not very greatly, 
from those of Bunsen. 

The principal and most important difference between 
the two groups is that of the quantity of silica, in which 
respect there really seems to be a kind of leap with most 
rocks. The basic rocks in general also contain somewhat 
more lime and magnesia than the acidic. 



Average Compositions 


of the two classes 


of Igneous Rocks. 




Basic Rocks 


Acidic Rocks 


Silica 


. 4555 


. 6080 


Alumina . ... 


... 1020 


816 


Protoxide | ofiron 


115 


V . 115 


Oxide J 






Lime 


.' 110 


15 


Magnesia . 


1 6 


4 


Potash . 


1 4 


1 6 


Soda 


1 5 


1 6 


Water . 


7 


8 



But the limits which we have above given are some- 
times overstepped on each side, and there are igneous 
rocks which we cannot with mere reference to their chemi- 
cal composition reckon in either group, and which in fact 
entirely fill up and annihilate the assumed gap between 
the two in respect of the content of silica. These rocks 
of middle character can only be classed with one group 
or the other by having regard in each case to their geo- 
logical character or their mineralogical affinities. 

If we disregard minor differences, the varieties of 
igneous rocks are not very numerous ; they may be 
almost reduced to two principal mineral combinations, 
the other differences consisting chiefly in texture or the 
presence of accessory or single minerals. 

The two principal combinations are as follows : 

(1) Felspar poor in silica (in its stead sometimes nephe- 
line or leucite) combined with pyroxene or hornblende, 
also mica, magnetic iron-ore, and the like. 

K 



130 IGNEOUS HOCKS. 

(2) Felspar rich in silica, combined with quartz, mica, 
and occasionally amphibole, and the like. 

In presenting this broad view, we do not mean to un- 
derrate the importance of the minor differences in the 
igneous rocks. All those differences are the result of 
varying conditions and circumstances of their original 
formation, and are therefore deserving of the greatest 
attention and study. 

We will return to this subject in the concluding chap- 
ter, and mention some of the theories in respect to the 
causes of the various development of the different igneous 
rocks. 



IGNEOUS ROCKS. 331 



BASIC IGNEOUS ROCKS. 

These are compounds of felspar (of various species) 
with augite, pyroxene, hornblende, or dark coloured 
mica. They frequently also contain magnetic iron- 
ore, sometimes olivine. In some rocks of this class 
nepheline or leucite takes the place of the felspar. In 
most, there is an entire absence of quartz. 

Their texture is compact, porphyritic, or crystalline ; 
granular, seldom fissile, more frequently vesicular, or 
amygdaloidal ; they are often found in a wackenitic state 
(wacke). 

According to our arrangement as previously indicated, 
we divide these rocks into two classes expressive of their 
origin viz. the volcanic and the plutonic. 

1. Volcanic. 

These rocks occur in the form of lava at actual vol- 
canoes of the present day ; they are also found in districts 
where the volcanoes to which they owe their birth have 
been long extinct. In the latter case they often form 
isolated conical mountains, or they are found as dykes 
filling up the rents and fissures of older rocks. 

They differ from the plutonic rocks (which have solidi- 
fied deep down in the earth) by the prevalence of a 
species of felspar poor in silica, such as labradorite (or in 
its stead nepheline or leucite) ; moreover, by the preva- 
lence of augite rather than hornblende ; and by the total 
absence of quartz in their composition. Volcanic rocks 
also show the traces of their former state of fusion much 
more distinctly than the plutonic ; and they have evidently 
cooled much more rapidly than them. 

All the volcanic rocks hitherto met with are of com- 
paratively recent date, and probably no ancient ones are 
now existing : for the most part they have decayed away. 

K 2 



132 BASIC IGNEOUS KOCKS. (l) VOLCANIC. 



BASALTIC KOCKS. 

These rocks are mostly compounds of labradorite and 
augite, with the addition of some magnetic iron-ore. 
Instead of the labradorite, they sometimes contain 
oligoclase, nepheline, leucite, or hauyne, and frequently 
also olivine. In their fresh state they are black or 
dark-grey. 

These rocks have been differently named, partly ac- 
cording to their somewhat varying mineralogical compo- 
sition, partly in respect of their differing texture. The 
most usual distinctive designations are the following : 

Dolerite, consisting of labradorite and augite. 

Nepheline-dolerite, consisting of nepheline and augite. 

Basalt, the same compound in a compact state. 

Leucite rock, consisting of leucite and augite. 

Besides the above, there occur other, though less fre- 
quent combinations, and varieties which have been 
separately named, or which deserve special notice as 
frequently recurring. In this category we may place 
anamesite, tholeite, analcymite, allogovite, hauynophyry. 

The basaltic rocks are all much alike in their outward 
form and bedding. They occur as lava at active or re- 
cently extinguished volcanoes. Sometimes they form 
conical hills, which are to be regarded as the kernels of 
extinct volcanoes whose outer coating has been washed, or 
has decayed, away. Again, they frequently form dykes, 
that is, they fill up clefts in older rocks, but in this case 
they usually appear to be connected with larger masses 
of a similar nature from which they have branched out. 
Where they occur as actual lava we usually find vesicular 
or scoriaceous varieties and tufa formations of correspond- 
ing composition ; but not the vitreous state. There can be 
no doubt that all these rocks are cooled products of igneous 
fusion, and that the process of their formation is con- 
tinued at the present day. The proof of this even in the 
case of the older ones may be found in the effect which 
they have often produced upon other rocks with which 
they came into contact while in a state of fusion. Those 
rocks frequently exhibit transmutations, for which the 
simplest or only explanation is the effect of heat ; such as 



BASALTIC ROCKS. 133 

local vitrefaction, change of their state of oxidation ; 
expulsion of their bitumen, or carbonic acid, change of 
their texture, or obliteration of their jointed structure. 
Sometimes also, but less frequently, the stratification of 
older rocks has been disturbed to a remarkable extent by 
the eruption of basaltic rocks. Again, the latter very 
often contain, near their margin, fragments of the rocks 
which they have broken through, and breccias have been 
formed in this way. 

The basaltic rocks, as purely volcanic, chiefly belong 
to the most recent geological period. They are never- 
theless found in many districts whose former volcanic 
activity has long since ceased, and where their bedding 
shows that they are older than some tertiary formations. 
The original surface of these older basaltic rocks is usually 
partly or entirely decomposed and washed away, and 
they partake somewhat of the nature of plutonic rocks, 
especially resembling certain greenstones of analogous 
mineral character, and actually forming transitions into 
the latter from the more genuine basaltic rocks. They 
appear to have undergone many changes of state through 
the influence of time and position. Their vesicular cavi- 
ties have become filled with new mineral substances 
(amygdaloids), internal decomposition or transmutations 
have taken place, carbonates, zeolites, and other hydrous 
minerals (formerly absent) have been formed, and are 
now intimately blended with, and actually form part of 
their composition ; or else their original fresh condition 
has become wackenitic. Hence we find that no sharp 
defining boundary exists between the volcanic and the 
plutonic rocks. It nevertheless is not a little remarkable 
that we do not know any rocks of undoubted basaltic 
character older than tertiary.* The case is the same with 
the trachytes and other volcanic rocks, and, generally 
speaking, we find that all the older igneous formations 
differ materially from the more recent, and more still from 
the most recent. This fact deserves attention, and seems 
to require more explanation than it has hitherto received, 
since we are authorised on other grounds to conclude that 

* Mr. Jukes believes the Rowley Rag basalt of the South Stafford- 
shire coalfield to be of Palaeozoic age (Geol S. Staff. Coal/ield, Geol 
Survey}. TRANSLATOR. 



154 BASIC IGNEOUS ROCKS. (l) VOLCANIC. 

volcanic agency has been at work in all periods of the 
earth's history, much in the same way as at the present 
time, and has always brought forth like products. What 
has become of those older products corresponding to the 
lavas and basalts of the present age ? Doubtless a great 
part may have perished from long exposure to the de- 
stroying influence of the atmosphere, or if more deeply 
buried, has suffered internal change ; nevertheless it was 
to have been expected that here and there (in old con- 
glomerates for instance) we should have discovered some 
blocks and boulders at least of genuine basalt. Strange 
to say, none have yet been found, at all events none 
whose character has been proved with certainty. We are 
aware that in England some basaltic and phonolitic boulders 
are said to have been found in Devonian strata, but these 
statements seem to require further confirmation.* 

1. DOLERITE and AKAMESITE. Mimesite, Ne- 
pheline-Dolerite, Trap in part. 

DOLERIT und AITAMESIT. Mimesit, Basaltischer Griinstein, 

Griinstein, Nephelin-Dolerit. (Germ.} 
DOLERITE, Haily. (Fr.} 

A crystalline-granular compound of labradorite and 
augite with some titaniferous magnetic iron-ore. In 
nepheline-dolerite, nepheline is a substitute for the 
labradorite. 

Spec. grav. . . . ... 2-7 2 -9 

Contains silica ..... 42 57 p. c. 

The name of Dolerite was given to this rock by Hau'y. 
It is rarely sufficiently coarse-grained to allow of its 
individual mineral constituents being readily distin- 
guished, but more usually it forms a fine-grained dark 
grey to black mass, in which we are unable to distinguish 

* In describing some of the igneous rocks interstratified with the 
Lower Silurian rocks of Ireland, Mr. Jukes mentions the occurrence of 
associated beds of conglomerate containing pebbles of vesicular trap, 
derived probably from the upper surface of the old lava flows (Student's 
Manual, 2nd Edit. p. 82). Some of the traps interstratified with the 
Carboniferous Limestone of Co. Limerick have the vesicular and quasi- 
scoriaceous parts of their upper and under surfaces preserved. A 
similar fact is described by Mr. Geikie in his paper on the trap rocks 
of Scotland (see Trans. JR. Soc. JEdm. vol. xxii. part 3, p. 641). 
TRANSLATOR. 



BASALTIC ROCKS. 135 

between the labradorite and augite. This fine-grained 
variety has been specially named by von Leonhard as 
Anamesite. 

If the compound is distinct, then the labradorite appears 
in the form of white or light-grey tabular crystals, the 
augite in black columnar ones. But in such case there 
is usually also a compact matrix in which the more dis- 
tinct particles are imbedded. This matrix is a compound 
of the same ingredients viz. labradorite and augite, 
usually with the addition of magnetic iron-ore, and some 
carbonate of protoxide of iron and carbonate of lime, and 
is so compact that its several components cannot be re- 
cognised with the eye, except that the magnetic iron-ore 
sometimes appears in distinct octahedrons. 

The presence of the carbonates of protoxide of iron 
and of lime of which we have spoken was first demon- 
strated by Bergemann, as well as that of a certain silicate 
of alumina and soda, whose character he could not defi- 
nitely determine. He showed that almost every dolerite 
contains one part capable of being decomposed by, and 
another part which resists the influence of muriatic acid. 
The first part consists of the carbonates, the magnetic 
iron-ore, and the undetermined silicate. The latter part 
consists of augite, and probably also some labradorite, 
inasmuch as the different kinds of labradorite comport 
themselves very variously in the presence of muriatic 
acid, and there is also a, material difference according to 
whether it be heated or not. Most kinds of dolerite con- 
tain from 1 to 2 per cent, of water, but this Bergemann 
regards as accidental, and as not having formed part of 
the original composition of the rock. 

Bergemann made a series of analyses to test the com- 
parative character of two kinds of dolerite, the one at the 
Meissner Mountain in Hessen, and the other at the 
Aulgasse in Siegburg in Westphalia, with the following 
result : 

Meissner Aulgasse 

Labradorite 47'91 . 30-06 



Augite 

Magnetic iron-ore 
Silicate (problematical) 
Carbonates 



9-27 

8-97 

22-21 

11-29 



35-43 
3-61 
2-71 

27-75 



We thus find two perfectly characteristic varieties of 



136 BASIC IGNEOUS KOCKS. (l) VOLCANIC. 

dolerite differing very widely in their mineralogical com- 
position. In other varieties, in spite of outward uniformity 
of appearance, other and even greater differences, both of 
mineral and chemical character, constantly occur. 

Besides the above-named more or less essential in- 
gredients of dolerite, it contains a considerable number of 
accessory ingredients, many of which are only locally 
found, or in very subordinate quantity. Such, for in- 
stance, are nepheline, sodalite, melanite, mica, bronzite, 
hornblende, olivine, titaniferous iron-ore, and specular 
iron. In fissures and vesicular cavities there also occur 
zeolites of various kinds, and distinctly crystallised sparry 
carbonates. 

In some varieties, the proportion of nepheline is very 
considerable, supplanting the labradorite, and so forming 
transitions into nepheline-dolerite. Becoming more com- 
pact in other varieties, dolerite passes over into basalt, 
and the different stages of compactness of texture may be 
typified by the three names of Dolerite, Anamesite, Basalt. 

Varieties in Texture. 
(a) COMMON DOLERITE. x j n w hich the principal ingredients 

G-EMEINERDOLERIT. (Germ.) \ M-nlisriTMtflirvimMo Tfloin Pm'oami 

DOLEHITE LITHOIDE. (Fr.) f ar e Distinctly visioie- -iviem-.rnesen, 

J near Tetschen, Bohemia. 

(5) ANAMESITE. } Fine-grained, the principal ingredients 

^^^on Leonhard. L on i y barely visible, Steinheim, near 
ANAMESFTE. (Fr.) ' Hanau. 



(c) PORPHYRITIC DOLERITE. \ With crystals of labradorite 

PORPHYRARTIGER DoLERTT. (Germ.) f onmfp ratlipr rVP 

DOLERITE PORPHYROIDE. (Fr.) ) 01 au g lte > rather rare - 

(d) VESICULAR or SCORIACEOUS DOLERITE. ) This texture only 

BLASIGER (or SCHLACKIGER) DOLERIT. (Germ.) f occurs in the tine- 
grained varieties (anamesite) ; frequent at volcanoes Stein- 
heim, near Hanau. 

(e) AMTGDALOIDAL DOLERITE. ) With filled-up cavities. 

MANDELSTEINARTIGER DOLERIT. (Germ.) r This variety is rather more 

AMYGDALOIDE. Brongniart. (Fr.) ) __ 

rdi t/. 

(f) DOLERITE-WACZK. ) Can in general only be recognised as 

DOLERIT WACKE. (Germ.) \ belonging to dolerite by tracing the 
WACKE DOLERITIQUE. (Fr.) j sequence of transition states, or by 
its immediate juxtaposition in nature with fresh dolerite. 

Variety in Composition. 

(g) NEPHELINE-DOLERITE. ] A crystalline granular compound 

NEPHELIN-DOLERIT, Von Leon- I of nepheline and augite with ti- 
' taniferous magnetic iron-ore. 



BASALTIC ROCKS. 137 

Spec. grav. . . . . 2-22-6 
Contains silica .... 41 61 p. c. 
This rock, formerly taken for common dolerite, was first sepa- 
rately described and named by v. Leonhard. It is a dolerite in 
which nepheline takes the place of labradorite. As accessories 
we find it to contain thin acicular crystals of apatite, some 
sanidine, olivine, and titanite. In becoming compact it passes 
into nepheline-basalt, which is hardly to be distinguished from 
common basalt. 

Subvarieties of Texture. 

(a) Porphyritic Nepheline-dolerite, the porphyritic texture being 
created by crystals of nepheline. Xatzenbuckel in the Oden- 
wald. 

(/J) Vesicular and amygdcdoidal and wackenitic varieties occur; as 
also fine-grained ones, answering to anamesite, e.g. in the 
Lobauer mountains. 

Perhaps much of what has hitherto been called dolerite is 
more properly nepheline-dolerite. The rock is now very 
distinctly recognisable, e.g. near Meiches in Hessen, at the 
Lobauer Berg in Upper Lausitz and near Tichlowitz on the 
Elbe in Bohemia. 

Dolerite is found irregularly massive, or of columnar, 
tabular, or globular jointed structure. It forms lava 
streams, isolated cones, and veins in other rocks. 

This rock is so frequent in all countries, especially in 
volcanic districts, that particular localities need not be 
further enumerated. We will only add that the doleritic 
trachytes of G. Rose, which are mentioned in the fourth 
volume of his ' Kosmos,' as occurring at Etna, Stromboli, 
&c., appear to be dolerites rather than trachytes. 

References. 

v. Leonhard, Basaltgebilde. 1832, vol. i. Nepheline in Do- 
lerite, 1822. 

Bunsen in Poggendorf s Annalen, vol. Ixxxiii. p. 197. 

Abich, Vulkanische Erscheinungen, 1841, p. 74. 

liergemann in Karsten's Archiv. 1847, vol. xxi. p. 1 and 41. 

/leusser in Poggend. Annalen, 1852, vol. xxxv. p. 299. 

G. Hose, On Dolerite, in Neumann's Zeitsch. f. Erdkunde, 1859, 
vol. vii. p. 265. 

Deluxe in Ann. des Mines, 1858 [5], vol. xiii. p. 369. 

Durocher in Ann. des Mines, 1841 [3], vol. xix. p. 659." 

Hartung, Die Azoren, 1860, p. 97. 

v. Roth in the Zeitschr. der deutsch geol. Ges. 1860, vol. 
xii. p. 40. 

Zirkel in the Zeitschr. der deutsch geol. Ges. 1859, vol. xi. 
p. 539, on Nepheline-Dolerite. 

Gumprecht in Poggend. Ann. voL xlii. p. 177. 



138 BASIC IGNEOUS EOCKS. (l) VOLCANIC. 

G. Rose in Karsten's Archiv. 1840, vol. xiv. p. 261. 

Schitt in v. L. andBr. Jahrbuch, 1857, p. 43. 

Lowe in Poggend. Annalen, 1836, vol, xxxviii. p. 158. 

Girard in Poggend. Annalen, 1841, vol. liv. p. 559. 

Heideprim in d. Zeitschr. d. d. geol. Ges. 1850, p. 149. 

Hesse in Journ. f. prakt. Chem. 1858, vol. Ixxv. p. 216. 

Mitscherlich, Basalt u. Nephelindolorit am Rhein. Zeitsch. d. 

deutschen geol. Gesellsch. 1863, p. 372. 
Otto Prolss, Analysen einiger Dolerite von Tava. Neues Jahrb. 

f. Miner. 1864, p. 426. 
v. Rath, Dolerite der Enganeen. Zeitschr. d. deutsch. geolog. 

Gesellsch. 1864, p. 496. 
A. Knop, Nephelindolerit von Meiches. Neues Jahrb. f. 

Mineralogie, 1865, pp. 674 and 682. 

Appendix. 

THOLEITE. Steininger has given the name of Tholeite to a rock 
found at the Schaumberg near Tholei, which he took for a 
compound of albite and titanite. But according to Berge- 
mann's analysis this rock consists of 70 labradorite, 5 augite, 
3 magnetic iron-ore, 11 of undetermined silicate, and 9 of 
carbonate of lime and protoxide of iron. It must therefore from 
its composition be considered a dolerite or basalt unless indeed 
it be considered as plutonic and classed with melaphyre. 

ANALCTMITE. ) Bergemann in Karsten's Archiv. 1847, 

CYCLOPHYRE, lle de Beau- [ vol. xxi. pp. 4, 12. Gemellaro has given 

mont. (Fr.) ) the name of Analcymite to a rock found 

in the Cyclades which appears originally to have been a dolerite 

containing nepheline, but two-thirds of its mass now consist of 

analcime, although the latter chiefly fills clefts and cavities. 

We may here also mention two kinds of volcanic rock which 
might collectively be called 

OLIGOCLASE-DOLERITE. We refer to the AKDESITE of L. v. Buch, 
and the TRACHYDOLERITE of Abich. 

Both are compounds of oligoclase, augite, hornblende, mag- 
netic iron and some mica, the latter generally of dark colour. 
But as their silica contents often exceed 60 per cent., and as 
they are frequently found in vitreous state but of trachytic ap- 
pearance, we have arranged them according to universal custom 
amongst the trachytes; but no doubt they stand on the 
boundary between the trachytic and basaltic rocks, and may be 
considered as transition states between the two. 

2. BASALT. Nepheline Basalt, Trap in part 

BASALT. (Germ.*) 
BASALTE. (Fr.) 

A compact rock, nearly or quite blacky with dull con- 
choidal fracture ; an apparently homogeneous com- 
pound^ of which the essentials are labradorite (or 
nepheline), augite, and magnetic iron-ore, frequently 



BASALTIC ROCKS. 139 

united with carbonates and zeolitic substances. In 
the compact mass there often occur prominently dis- 
tinct grains or even crystals of olivine, labradorite, 
augite, and magnetic iron-ore. 

Spec. grav. . . . . ,' ' . 2'9 3-1 
Contains silica . . . . . 40 5G p.c. 

The mineral ingredients of basalt are too small and 
intimately blended to be separately recognised with the 
naked eye ; formerly it was taken to be a simple mineral 
substance, but it is now shown to be only the compact 
state of dolerite or nepheline-dolerite. We must, however, 
observe that olivine and magnetic iron-ore is of much 
more frequent occurrence in basalt than in the two last- 
named rocks. 

Cordier was the first who, by means of microscopic 
examination, thought he recognised in basalt a similar 
composition to dolerite. Hessel confirmed this view by 
deduction from analysis, and many instances of the 
gradual transition from basalt into dolerite also coincided. 
But that basalt was in fact a compound of the above- 
named minerals was afterwards established beyond doubt 
by the more accurate analyses of Gmelin, Lowe, Girard, 
v. Bibra, Grager, Binding, Petersen, Ebelmen, Baumann, 
Rammelsberg, Schmid, and Bergemann. 

Gmelin first found that a portion of the mass of basalt 
was soluble in muriatic acid, and another portion not. The 
insoluble part he considered must be chiefly augite and 
olivine, perhaps also labradorite ; the soluble part, mag- 
netic iron-ore, a sparry carbonate and zeolitic substance 
(and sometimes nepheline). The proportion between the 
two parts (as in the case of dolerite) is very different in 
different kinds of basalt. The quantity of the soluble por- 
tion fluctuates between 36 and 88 per cent. The propor- 
tion of the individual mineral constituents, and also that of 
the elementary ingredients, appear to be equally variable. 

Like dolerite, basalt very often contains some carbonate 
of iron, calcspar, and zeolitic substance (probably arisen 
from decomposition, and of later date than the rock itself) 
and some kinds of basalt likewise contain nepheline 
instead of labradorite. Girard first discovered this com- 
position in the basalt of Wickenstein in Silesia. It is 
not easy from outward characteristics alone to distinguish 



140 BASIC IGNEOUS ROCKS. (l) VOLCANIC. 

the nepheline-basalt from the ordinary species, unless we 
are assisted by finding a transition into a distinct nephe- 
line-dolerite, as is the case, for instance, at the Lobauer 
Berg. For this reason it is hardly practicable for the 
geologist to separate nepheline-basalt from labradorite- 
basalt as a distinct rock, although the difference between 
them, in a purely mineralogical point of view, is of more 
importance than that between dolerite and basalt, which 
are only varieties of texture of the same mass. 

Besides the more or less essential ingredients of basalt 
(to which we therefore reckon nepheline), other minerals 
also very often occur as accessories porphyritically dis- 
seminated through the mass. Thus, for instance, basaltic 
hornblende, oligoclase, dark brown mica, rubellan, zircon, 
(hyacinth), sapphire, apatite, garnet, bronzite, micaceous 
iron, titaniferous iron-ore, pyrites, &c. These minerals 
may, in consequence of special local circumstances, have 
either developed themselves into crystals during the 
original cooling of the rocks, or (such as pyrites and 
micaceous iron) they may have arisen from later processes 
of transmutation. Similar internal transmutations aided 
by gases or water have most probably produced the car- 
bonates, zeolites, and water concealed in the compound. 
The same influences have, doubtless, also produced the 
minerals which have arisen in the vesicular cavities and 
narrow fissures of the rock, such as hyalite, chalcedony, 
zeolites, sparry carbonates, glauconite, &c. 

The essential texture of basalt is compact ; if it becomes 
crystalline-granular it passes into anamesite and dolerite. 
But we frequently find porphyritically disseminated in 
the compact base, numerous single crystals or crystalline 
grains of augite, hornblende, olivine, magnetic iron-ore, and 
the like, or the rock is penetrated with vesicular cavities, 
and these are filled with those newer mineral formations of 
which we have already spoken. There also often appears 
a kind of round-grained or spotted conformation which 
seems to be the result of decomposition. 

Varieties in Texture. 



( " } Very frequent e.g., at SchlossHerg, 



(Germ.) near otolpen, Saxony. 

BASALTE LTTHOIDE. (Fr.) 



BASALTIC EOCKS. 141 

(6) PORPHYRITIC BASALT, or BASALTIC \ .. _ 

PORPHYRY I Aiso f re( l uent Leschtma, 

BASALTE poRpHYRotoE. (Fr.) ) Q ear Tetechen, in Bohemia. 

PORPHYRAKTIQER BASALT. (Germ.) ' 

(c) VESICULAR or SCORIACEOUS BASALT. ) Often called, par excel- 

SCORIES BASAL-PIQUES. (Fr.) [ Icticc, Basaltic Lava, as 

BLASIGER ODER SCHLACKIGER BASALT. (Germ.) J t his j s usua lly vesicular 

at the surface Kammerbiihl and Wolfsberg, in Bohemia. 

(d) AMYGDALOIDAL BASALT, or BASALTIC i Never of recent origin 

AMYGDALOID. J Schlachenwerth, near 

BASALTE AMYGDALOIDE. (Fr.) I Carlabad 

MANDELSTEIXARTIGEH BASALT. (Germ.) 

(e) SPOTTED AND GRANULAR BASALT \ Usually has dark grains in 

(RESEMBLING DOLERITE). I lighter green mass. It is 

KORXIOFLECKIGERODERDOLENTAHNLICHER [ a Stage of decomposition 

J E.g. between Arnsdorf and 
Steinschonau, in Bohemia, as Stoppels Kuppe, near Eisenach. 

(f) BASALT- WACKE. ) (Werner's Eisenthon) a dark brown 

\V.\CKK BASAI.TIQCE. (Fr.) \ OT grev, almost earthy mass, in which 
BASALT- WACKE. (Germ.) ) sometimes the textures (a) (6) (c) and 
(d) are distinctly repeated. Pascepole, near Teplitz. 

Sometimes, but quite exceptionally, a vitreous state also occurs, 
which Breithaupt has named Trachylyt, as a separate mineral 
formation. It is found, e.g. near Dransfeld, in the Vogelsgeberg 
and skirting basalt-veins in Iceland. 

Here may be also fitly mentioned a number of varieties 
of composition, some of which, if they were always dis- 
tinguishable, might even be separately classed as distinct 
rocks. 

Varieties in Composition. 

(c/) COMMON (or LABRADORITE) BASALT. ) Consisting of labradorite, 
LABRADOR BASALT. (Germ.) i augite, magnetic iron- 

ore, and usually also some olivine. 

(A) NEPHELINE-BASALT. \ In which nepheline is substituted for la- 

NEPHELIN-BASALT. I bradorite ; according to Girard, it shows 

BASALTEAVEC NEPHE- ( traces of a resinous lustre, and thereby dif- 

LINE. (Fr.) ) fers somewhat from ordinary basalt. But 

there must be intermediate gradations or transitions between 

the two which cannot be distinguished as separate varieties. 

() HAUYNOPHYRY. \ Is the name given by Rammelsberg 

HAUYNOPHTR, Rammel&erg. f to a rock from Vulture, near Melfi, 

HAtJ^oP^RE. (fr.) f not far from Naples, which essentially 

/ consists of augite and haiiyne, with 

some olivine, mica, and leucite, in which also the haiiyne ap- 
pears to be the substitute for the labradorite of basalt or 
dolerite. The simultaneous occurrence of leucite, however, 
causes it to resemble leucite rock. 

The basaltic lava of Niedennendig on the Rhine contains a 
considerable quantity of haiiyne distinctly prominent, but it 
has been conjectured that this rock according to its conipo- 



142 BASIC IGNEOUS ROCKS. (l) VOLCANIC. 

sition should belong to the nepheline-basalt. On account of its 
vesicular conformation it is well adapted for millstones. 

(&) ALLOGOVITE. -j Is the name given by Winkler to certain 

ALLOGOVIT, Winkler. \ dark grey or reddish rocks of the Allgau, 
' which according to him are formed of an 
intimately blended compound of labradorite with the basalts, 
although their colour is somewhat different. This may, how- 
ever, be the consequence of a slight difference in composition 
or an incipient decomposition. 

Regular jointed structure is very frequent in basalt, 
usually columnar, sometimes however tabular or spherical, 
with concentric layers spheroidal, or even irregularly 
massive. It forms streams of lava and layers in the 
basaltic tufa. It is very characteristically and variously 
developed in the Bohemian Mittelgebirge ; in the 
columnar form it may be seen with great regularity and 
beauty at the Giant's Causeway in Ireland, at Staffa, &c. ; 
but these approach dolerite in their character, and may 
be more accurately described as transition states between 
that rock and basalt. 

References. 

v. Leonhard, Basaltgebilde, 1832, vol. i. 
A. Madelung, Metamorphosen von Basalt und Chrysolith. 

Jahrb. der geol. Reichsanst. 1864, vol. xiv. p. 1. 
Abichj Vulkanische Bildungen, 1841. 

Bergemann, Analysen in Karsten's Archiv. vol. xxi. p. 88, 1847. 
Surtorius v. Waltershausen, Physik. geogr. Skizze v. Island, p. 64. 
Schmid, Analysen in der Zeitschrift d. d. geol. Gesellsch. vol. v. 

p. 280, 1853 ; and Poggend. Annalen, vol. xcix. p. 291, 1853. 
Rammelsberg in der Zeitschrift d. d. geol. Ges. p. 493, 1859 j 

p. 273, 1860 ; p. 4, 1861, iiber Hauynophyr. 
Schitt in v. Leonhard u. Br. Jahrb., p. 44, 1857 (Hegau), and 

in G. Leonhard's Beitr. z. miner. Kenntn. von Baden, No. 3, 

p. 43, 1854 (Kaiserstuhl). 
Hartung, Die Azoren, j). 97, 1860. 
Girard, Ueber Nephelinbasalt in Poggend. Annalen, vol. liv. 

p. 562, 1841. 

3. LEUCITE ROCK. Leucite- Porphyry, Leucito- 
phyry, Leucilite, Sperone. 

LETJCITFELS. (Germ.) 
LEUCITOPHYRE, Coquand. (Fr.) 

A more or less distinct compound of Icucite and augite, 
with some magnetic iron-ore porphyritic or compact. 

Spec, grav 2-5 2-9 

Contains silica. . . . . . 45 54 p. c. 



BASALTIC EOCKS. 143 

Leucite rock may be regarded as a dolerite, in which 
the labradorite is replaced by leucite. This difference of 
composition is also usually accompanied by other differ- 
ences easily to be recognised. The colour of the compact 
mass or matrix of the rock is more grey or reddish-grey 
than either dolerite or basalt, and, moreover, the charac- 
teristic crystals of leucite are frequently to be found dis- 
tinctly and prominently developed. It is a distinguishing 
feature of this mineral in general, that it rarely occurs 
otherwise than porphyritically imbedded, and not clus- 
tered in geodes. Sometimes distinct crystals of augite 
lie near the leucite in the compact matrix. As acces- 
sories leucite rock also contains the following minerals : 
dark magnesia-mica, sodalite, sanidine, labradorite, ne- 
pheline, olivine, haiiyne, garnet, and traces of apatite. 
Zeolites also very frequently occur in the clefts or vesi- 
cular cavities of this rock. 

Where the proportion of nepheline is greater, a transi- 
tion takes place into nepheh'ne-dolerite or nepheline- 
basalt. 

Varieties in Texture. 

(a) PORPHYRITIC LEUCITE, LEUCITOPHYRY. 

LEUCITOPHYRE PORPHYROXDE. (Fr.) 
(6) COMPACT LEUCITE. 

LKUCTTOPHYRE LITHOKDE. (Fr.) 

(c) VESICULAR or LEUCITE-LAVA. 

LEUCITOPHYRE VACUOLAIRE. (Fr.) 

(d) AMYGDALOID. 

AMYGDALOlDE. (Fr.) 

Leucite rock forms old and recent lavas, e.g. at Monte 
Somma and at Vesuvius (eruptions of 1828 and 1832); it 
also occurs at volcanoes long extinct, for instance at 
Roccamonfina, in the Albanian Mountains, at Bieden, 
and at Bell near Andernach. Not long since, a leucite- 
porphyry was discovered at Bohmisch-Wiesenthal, on the 
highest ridge of the Erzgebirge, with decomposed wack- 
enitic matrix, and crystals of leucite, more than an inch 
in length, but for the most part changed into orthoclase 
(or kalioligoclase). This last named occurrence involun- 
tarily suggests the question whether the felspar of many 
older rocks may not originally have been leucite, whose 
form has become indistinct or entirely altered so as to be 
no longer recognised. It certainly is somewhat remark- 
able that hitherto no ancient leucite rock has been found. 



144 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

Appendix. 

NOSEAN-MELANTTE ROCK is the name recently given by vom Rath 
to a rock consisting of a fine-grained compound of nosean, 
vitreous felspar, and melanite, with some hornblende, augite, 
and titaniferous iron-ore. Zeitsch. der deutsch. geol. Ges. 
p. 655, 1862. 

Von Fritsch uses the common name of TEPHRITE to include leuci- 
tophyry, hauynophyry, and nepheline rock. Neues Jahrb. f. 
Mineral. 1865, p. 663. 

DUNITE is the name given by von Hochstetter to a granular rock 
which occurs in New Zealand, consisting almost exclusively of 
olivine. Zeitschr. d. deut. geol. Ges. 1864, p. 341. Sand- 
berger has described a similar rock as occurring in the Tring- 
stein in Nassau. Neues Jahrb. f. Mineral. 1865, p. 449. 

References. 
ie la Soc. d. 
Dufrenoy, Mem. p. s. a un descr. geol.'d. Fr. vol. iv. p. 368. 



Devitte in the Bullet, de la Soc. d. Fr. [2] vol. xii. p. 612, 1856. 

E. s. a un descr. geol. d. Fr. vol. iv. 
xxi. p. 326, 1845. 



Wedding in d. Zeitschr. d. d. geol. Ges. vol. x. p. 395, 1858. 
v. Rath in d. Zeitschr. d. d. geol. Ges. vol. xii. p. 37 (Zittau), 

1860. Leucitophyr von Rieden : Zeitschr. d. deutschen 

geol. Gesellsch. 1864, p. 73. 
Naumann in v. L. und Br. Jahrbuch, p. 61, 1860 ; p. 59, 

1861 (Wiesenthal). 
Rammelsberg in d. Zeitschr. d. d. geol. Ges. vol. xi. p. 493, 

1859 ; vol. xiii. p. 96, 1861 (Vesuv. and Wiesenthal). 

2. Plutonic. 

These rocks are compounds of various felspars with 
pyroxene, hornblende or mica. Besides these essential 
ingredients they frequently contain some chlorite, nephe- 
line and magnetic iron-ore, quartz only exceptionally ; 
the greater number are free from quartz. Mineralogi- 
cally as well as chemically, therefore, the composition of 
these rocks is very similar to that of the basaltic rocks. 
The chief differences consist in the greater frequency of 
hornblende as an essential ingredient, and the frequent 
occurrence of chlorite and the more rare occurrence of 
quartz as accessories ; and in the development of slaty or 
schistose texture in many of these plutonic rocks. 

All these differences may be accounted for by the 
greater depth at which these rocks probably attained the 
solid state, and by their having remained a longer time 
under the pressure of superincumbent masses. The same 
causes may have given rise to many transmutations or 



GREENSTONE GROUP. 145 

new formations, such for instance as the formation of 
chlorite, a characteristic (if not altogether essential) in- 
gredient of the augitic greenstones, and to which they 
chiefly owe their green colour, and which also usually 
serves to distinguish them from the basalts. 

TVe divide the plutonic basic rocks into GREENSTONES, 
MELAPHYRES, PORPHYRITES, MICA-TRAPS and SYE- 
NITES. Some of these, however, approach the acidic 
rocks in the proportion of silica which they contain. 

GREENSTONES (trap in part). 

These rocks are compounds of some species of felspar 
with pyroxene or hornblende as essential ingredients ; 
their prevailing dark green colour they apparently 
owe partly to hornblende and partly to a small admix- 
ture of chlorite. 

They are usually divided according to their mineral 
character into three classes, under the following heads : 

Diabase, consisting of felspar and hypersthene or augite 
and chlorite. 

Gabbro, consisting of felspar and pyroxene. 

Diorite 9 consisting of felspar and hornblende. 

Besides these principal divisions, there are several 
subordinate varieties of composition which have distin- 
guishing names, such as Calc-diabase, Eukrite, Teschi- 
nite, Augite-rock, Malakolite-rock, Euphodite, Norite, 
Hypers thenite, Timazite, Calc-diorite, and Anorthite- 
diorite. Aphanite is the compact state of greenstone 
rock in which the several ingredients are not to be distin- 
guished with certainty ; and if the compact aphanitic mass 
contain distinct individual grains or crystals porphyriti- 
cally disseminated through it, then we employ the names 
of Calc-aphanite, Labradorite-porphyry, Oligoclase-por- 
phyry, Augite-porphyry, and Uralite-porphyry, for the 
different varieties. 

Greenstones of all kinds occur frequently in subor- 
dinate masses, dykes, or stratified veins in the schists or 
slates of the grey-wacke or transition period, and even 
alternating with tuff-formations of the same period which 
contain characteristic fossils, so that we may conclude 
that many greenstones were contemporaneous with those 
formations. This association with the transition-forma- 

L 



146 BASIC IGNEOUS EOCKS. (-2) PLUTONIC. 

tions may be observed in the Voigtland, Fichtelgebirge, 
Hartz, and the Rhine district, also in the Silurian district 
of Bohemia, in Germany, and many other parts of the 
world. Greenstones are likewise met with which have 
broken through and penetrated much more recent forma- 
tions; the timazite of Hungary and Transylvania for 
instance is found to have even penetrated sandstones of 
the tertiary period. But the most recent tertiary for- 
mations are nowhere found to have been broken through 
by genuine greenstones, although very frequently by 
basaltic rocks. Greenstones are never found in the form 
of genuine lava, but always more or less show their 
plutonic origin, in which probably consists the whole 
difference (not very considerable after all) between them 
and the basalts. It is very possible that the same basic 
compound which, consolidating near the surface, has pro- 
duced the basaltic rocks, when it attained the solid state 
at a greater depth formed the greenstones, whose pyrox- 
ene and hornblende may have been partly an original 
product and partly produced by subsequent transmu- 
tation. The basalts and greenstones in general very much 
resemble each other both in chemical composition and 
mineral character. The chlorite, by which some of the 
augitic greenstones are alone distinguishable from the 
basalts, is most usually a product of transmutation. 

4. DIABASE. Hyperite, Scandinavian Trap. 

DIABAS. (Germ.} 

DIABASE, Brongniart. (Fr.} 

A crystalline-granular compound of oligoclase, labra- 
dorite, albite, or anorthite, with pyroxene and some 
chlorite in its fresh state dark green. 

Spec.grav 2-72-9 

Contains silica . . . . . , 43 56 p. c. 

Diabase was first raised to the rank of a separate rock, 
and distinguished from other greenstones, by Hausmann. 

It is often very fine-grained, and in that case it be- 
comes difficult to determine the , species of the felspar or 
of the pyroxene, or to recognise the chlorite as such. 
The felspar seems in most cases to be a white or greyish- 
green, oligoclase or labradorite. The pyroxene is most ge- 
nerally hypersthene, but sometimes common augite. The 
green colour of the rock is chiefly owing to its chlorite, 



GREENSTONE GROUP. 147 

the quantity of which is however small. As accessories 
the following minerals very frequently occur : magnetic 
iron-ore, magnetic pyrites, pyrites, sometimes also some 
chalcopyrite (copper pyrites). 

As accessory accompaniments (in clefts, veins, nests and 
vesicular cavities) are found quartz, actinolite, asbestus, 
cat's-eye, pistacite, prehnite, axinite, calcspar, brownspar 
(dolomite), talcspar (magnesite), &c. 

The prevailing texture of diabase is fine-grained; it 
passes over into the compact (aphanite) ; it is also some- 
times porphyritic, slaty, variolitic or amygdaloidal. 

Diabase bears a strong relationship to dolerite, the 
most marked feature of its difference from the latter is its 
chlorite and its consequent green colour. If this chlorite 
be a product of transmutation, then all the original dif- 
ference between diabase and dolerite probably consists in 
the level or depth of solidification. 

The vesicular cavities of diabase (where they occur) are 
almost always filled up (amygdaloids), and this circum- 
stance may be explained by the rock having long lain 
in the interior of the earth under modifying hydro- 
plutonic influences. 

Varieties in Texture. 
(a) GRANULAR DIABASE j Frequent near Berneck, Saalburg, 

SSSZS!^ a 3ti [ both* in the Fichtelgebirge, &c. 
(6) FINE-GRAINED (TO COMPACT) DIABASE.) Merging into aphanite, 
FKiNKoijvioERBisDicHTEnDxABAs. (Germ.) > generally occurs with 
DIABASE LrraoStDE. (Fr.) j (a). 

(c) PORPHYRITIC DIABASE. ) In fine-grained base, crystals of 

PonpHYRARTiGERDiABAR.(G'erm.) I labradorite, 
DZABAHK POKPHVHO^ (Fr.) 



is compact, then these varieties are also sometimes designated 
labrador-porphyry, augite-porphyry, or uralite-porphyry (com- 
pare with aphanite, post, p. 157). 

(d) SCHISTOSE DIABASE, or DIABASE- ) Indistinctly foliated, going 

SCHIST. I over into aphanite-schist : 

DiABAs-ScHiEFKR. (Germ.) [ occurs together with (a) and 

SCHISTE DIABASIQUK. (f*r.) ) /\ 

(e) AMYGDALOIDAL DIABASE, or\ The vesicular cavities are filled 

DIABASE AMYGDALOID. I with calcspar, chlorite, glauconite, 
AM^l^iL^ 1 ^; (Germ ' ) > chalcedony and the like. Berneck 

in Fichtelgebirge. 

(f) VARIOLITIC DIABASE (VARIOLITE) In the principal mass round 
in part). I concretions occur of a com- 

VARIOI.ITISCHER DIABAS. (Germ.) [ pact or radial-fibrous or con- 
(Fr.) J centric felsite (labradorite), 

L 2 



148 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 

very characteristic near Berneck, where the small felsitic glo- 
bules have a violet-coloured nucleus and a white ring. 
0) WACKEIQTIC DIABASE, or ) Decomposed, discoloured, earthy, 
DIABASE WACKE. L an d can only be determined to be 

DIABAS-WACKE. (Germ.) \ such by its juxtaposition with other 
WACKE DIABASIQTJE. (Fr.) J diabase. 

The following rocks are varieties of diabase in respect 
of their composition, or are to be classed under the head 
of diabase on account of their close approximation. 

Varieties in Composition. 



CALCAREOUS DIABASE. } In the fine-grained or compact matrix 
KALKDIABAS. (Germ.) [ O f diabase rock are found small rounded 



. ) 



(h) COMMON DIABASE. 
(0 

DIABASECALCAIKE.(/V.) 

to be the fillings-up of cavities. This somewhat proble- 
matical variety has been called calc-trap by Oppermann. By 
others it has been called blatterstein, calc-aphanite, diabase, 
and amygdaloid, and if somewhat slaty, schalstein. (Loben- 
stein in the Fichtelgebirge.) 

(&) EUKRITE. ) A crystalline-granular compound of anor- 

ETJKRIT. (Germ.)) thite and augite, occasionally with some 
olivine, hornblende, and epidote. The latter appears to have 
arisen from decomposition. 

This rock, according to its mineralogical composition, would 
almost appear to be better classed with dolerite than diabase, 
but according to Tschermark and Kraff't, its geological cha- 
racter is plutonic. 

It appears at Gumbelburg near Neutschin in Moravia. Some 
meteorites have precisely the same composition. 
(I) TESCHINITE. \ Is the name given by Hohenegger to a 

TESCHINIT, Hohenegger. f rock whose mass is chiefly felsitic, and 
in which hypersthene forms long black 
needles ; it sometimes also contains fine needles of apatite. 
This rock has broken through chalk formations and even 
eocene strata in the neighbourhood of Tetschen, where it some- 
times forms irregular masses, sometimes veins. According to 
von Hochstetter, hornblende and augite form part of its com- 
ponents, also sometimes augite and labradorite with subordi- 
nate admixtures of iron pyrites, magnetic iron-ore, mica, and 
chlorite. These therefore are compounds which might partly 
be classed with the diorites and partly with diabase, hyper- 
sthenite, or even dolerite. 

More by way of appendix than as properly inclusive in 
this class, we here add : 

(m) AUGITE ROCK (LHERZOLITE). j A granular to compact ag- 

AUGITFELS, LHERZOLITH. (Germ.) i grearate, chiefly consisting of 

LHERZOLITE. (Fr.) ) l n ^ dttk^tt^ brown, or 

grey ; as accessory components it contains some talc, steatite, 



GREENSTONE GROUP. 149 

schorl, hornblende, or calcspar. This rock can only be said to 
be allied to diabase ; it forms subordinate masses at the Lake 
Lherz, near Vicdessos in the Pyrenees. [According to Damour, 
however, this rock of the Lherz is not thus composed, but 
consists of olivine, eustatite, and diopside. See Neues Jahrb. 
f. .Mineral. 1863, p. 95.] 

(ti) MALAKOLITE. j Found in granular limestone near 

MALAKOLTTHFELS. (Germ.) \ Rocklitz at the foot of the Rie- 
PvRoxfiNrrK, ^uand. (Fr.)> sengebirge) where> according to 

Herter and Porth, it forms subordinate masses, containing 
copper-ore and consisting essentially of compact salite (rnala- 
kolite). 

The diabases and the last mentioned rocks, which are 
related to them, are either found in indefinite masses or 
with columnar, spherical, or irregular spheroidal jointings. 

The genuine diabases are most frequently found in 
the Devonian, Silurian and Cambrian formations, so for 
instance in the Voigtland, Fichtelgebirge, and Hartz 
mountains, where sometimes the immediately adjoining 
clay -slate is transfonned into a kind of hornstone. 

References. 

G. Rose on Greenstones in Poggend. Annalen, 1835, vol. 

xxxiv. p. 1. 

Oppermann, Dissertation iiber Schalstein und Kalktrapp, 1836. 
IIiiHsmann, Ueber die Bildung des Harzgebirges, p. 22. 
v. Rodham u. Canaval, Kalktrapp oder Schalstein in Karn- 

then in v. L. u. Br. Jahrbuch, 1855, p. 584. 
Genth on Eukrite in the Annalen der Chemie u. Pharm. 1848, 

vol. Ixvi. p. 17. 
II(i/f(/hton on Eukrite in the Quarterly Journ. of the Geol. Soc. 

1856, vol. xii.j). 197. 
Tschermack u. &rafft., on Eukrite in the Berichten der Wiener 

Akademie, pp. 40 and 127. 
Hoheneyyer on Teschinite in Die geog. Verhaltnisse der 

Nordkarpathen, 1861, p. 43. 
v. Hochstetter on the same subject on the Jahrbuch d. geol. 

Preichsanst, 1853, p. 319. 
V. Charpentier on Augite Rock in his Essai sur la const. gtSol. 

des Pyrenees, 1823, p. 245. 
Marrout on Augite Rock in the Ann. des Mines, 1828 [2] 

vol. iv. p. 307. 
Herter u. Porth on Malakolite in the Jahrbuch der geol. 

Reichsanst, 1859, p. 10. 

Kjenilf (Diabase) in Christiania Silurb. 1855, p. 26. 
Delesse (Diabase) in the Ann. des. Mines, 1858 [5] vol. xiii. p. 

374. 
Modelling. Uber Teschinit. Neues Jahrb. fur Mineral. 1865, 

p. 345. 



150 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 

5. GABBKO. 

GABBRO, von Such. (Germ.} 
GABBRO. (-Fr.) 

These rocks are compounds of labradorite or saus- 
surite, with diallage, smaragdite, or hypersthene, 
and usually some other minerals. They are distin- 
guished by the irregularity oj their composition and 
texture. 

Spec. grav. '. ' . . , . . 2-8 3-1 
Contains silica ...... 43 46 p. c. 

The Italian name of Gabbro, which L. v. Buch first 
applied to a distinct class of rocks, has a broad and a 
narrow signification ; but as even the narrower meaning 
is not very definite, the name is more serviceable in its 
comprehensive sense, and in which it is more generally 
understood. 

Naumann, using the term in its narrower sense, de- 
scribed gabbro as a compound of labradorite or saussurite 
with diallage and smaragdite, and he separates from it 
hypersthene rock or hyperite, which essentially consists 
of labradorite and hypersthene ; and there are some very 
similar rocks which have received the names of norite and 
euphotide. 

All these in fact only form varieties of the same rock ; 
they are very difficult to distinguish from each other 
when they occur in a somewhat fine-grained state ; and 
when they pass over into the quite compact state, as is 
often the case, they all become aphanite. 

Since the texture of these rocks frequently changes 
very rapidly, that is within a small area, from very coarse- 
grained to fine-grained, compact, or slaty, their division 
into varieties of texture cannot serve any useful purpose. 
We shall therefore only enumerate the varieties of com- 
position, which are the following : 

Varieties in Composition. 

(a) GABBRO, DIALLAGE ROCK, GRANITONE. } Consists of labra- 
GABBRO. (Germ.) L dorite or saussurite 

DIALLAOITE, Descloizeaux. (/>.) 



ragdite irregularly combined, also sometimes of all those mi- 
nerals together. It is very coarse-grained, fine-grained to 
compact, sometimes slaty or spotted (variolitic). 



GREENSTONE GROUP. 151 

The felspar if in the form of labradorite is coarse-grained to 
fine-grained ; colour white, grey, or violet. If it be saussurite 
it is compact and white or greenish. 

The diallage occurs in white individual crystals of half 
metallic lustre, grey to green. The smaragdite is grass-green, 
and has a mother-of-pearl lustre. Small quantities of sparry 
carbonates are often also contained in the compound frequently ; 
not visible, but recognisable through effervescence with acid : 
they are probably of secondary origin. The visible accessory 
ingredients are mica, talc, hornblende (especially at the mar- 
gins of the diallage), actinolite, garnet, iron pyrites, magnetic 
iron-ore, titaniferous iron-ore, specular iron, and apatite. Many 
of these also may be secondary formations. Calcspar and 
quartz occur in nests or veins. 

This rock passes into serpentine by transmutation (as near 
Siebenlehn in Saxony) into aphanite by becoming compact, 
and apparently it also even passes into diorite, diabase, granite, 
and granulite. 

The prevailing character of gabbro is massive. It penetrates 
older rocks and formations in a massive form, or in the form of 
veins forms apparent parallel strata in such. But it is also fre- 
quently penetrated by veins of granite, which in that case gene- 
rally contain some orthite, as near Rosswein and Bb'hrigen in 
Saxony. In the Radauthal in the Hartz, where it may be easily 
mistaken for diabase, it also contains wollastonite, schillerspar, 
and rutile, and in fissures also desmine, prehnite, and albite, 
near La Prese in Upper Italy. It consists, according to Breit- 
haupt, principally of hornblende with metallic pearly lustre 
(schillerspar), and a felspar of the highest spec. grav. with 
some brown mica. If the felspars have become much wasted 
from weathering, then the pyroxenic ingredients often appear 
above the surface in strong relief. 
(6) EUPHOTIDE. | The euphotide of French geologists is 



Kri-Honrr. (Germ.) according to Delesse, essentially a com- 
BupH<mHB,ir*. </*..)) bination 6 of felspar and diallage with 
titaniferous and chromic magnetic iron-ore, iron pyrites, ser- 
pentine and carbonates. The felspar is Saussure's jade, which 
afterwards Beudant called saussurite. It approaches in cha- 
racter labradorite, also vosgite and anorthite. The diallage 
often occurs as the variety smaragdite, which, according to 
Haidinger, properly consists of a combination of hornblende 
and pyroxene. The talc forms small laminae, scarcely percep- 
tible, the serpentine minute veins. The carbonates consist of 
invisible particles of calcspar, dolomite, and iron. As acces- 
sories there also occur hornblende, mica, and garnet, especially 
characteristic in the Alps and in Corsica. 

(c) NORITE. i The norite of Scheerer (not of Esmark) is a 

NOWT, Scheerer. \ compound of hypersthene or diallage, labra- 
' dorite, orthoclase (containing soda), and even 
some quartz. 

The felspathic ingredient of this rock is sometimes so pro- 
minent that the whole mass almost appears to be nothing but 



152 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

a granular felspar rock. It occurs on the island Hitteroe, 
Norway. 

(d) HYPERSTHEISTITE, HYPERITE. "j Consists of a coarse-grained to 
HYPERSTHENIT, HYPERSTHENSYENIT, >. compact compound of labrado- 
(FrT } J. rite ^ d hypersthene. 

Labradorite is the prevailing ingredient, coarse to fine- 
grained, grey, greenish or bluish. The hypersthene appears 
dark-brown, to green on its cleavage surfaces, has a metallic 
pearly lustre, its outer edges sometimes coated with horn- 
blende. The labradorite is the most strongly affected by 
weathering, and it decays away, leaving the hypersthene to 
protrude. The following minerals occur as accessories in this 
rock : Titaniferous iron-ore, garnet, hornblende, olivine, brown 
mica, needles of apatite, iron pyrites, and magnetic iron-ore. 
It usually is of a massive structure, and forms veins or irregular 
masses between other rocks. It occurs characteristically in 
Hollenmiihle, near Penig in Saxony, Neurode in Silesia/ Isle 
of Skye, Elfdalen in Sweden. 

The monzon-hypersthenite of v. Richthofen differs slightly 
from the ordinary kind. It consists of a very distinctly crys- 
talline granular compound of dark-green to black hypersthene 
with greenish-white labradorite. The hypersthene is usually 
the principal ingredient ; sometimes, however, the labradorite 
is entirely predominant, and in that case distinct crystals of 
common black augite occur in the mass. 

The hypersthenic varieties also sometimes contain the like 
in small quantities, also dark -brown mica-plates and crystals 
of titaniferous iron-ore are found. At Monzoni in Southern 
Tyrol, this rock has broken through genuine syenite (free from 
quartz) and formed veins in it. 

References. 

v. Such in the Magaz. d. Gesellsch.-naturforsch. Freunde zu 
Berlin, 1810, vol. iv. p. 128. 

v. Rath in Pogg. Annal. 1855, vol. xcv. p. 535 (Silesia). 

Delesse, Bullet, de la Soc. geol. de France, 1849 [2] vol. vi. 
p. 410, 435, 547, and Ann. des Mines, 1849 [4] vol. xvi. p. 323. 

Scheerer in the Gaea Norwegica, vol. ii. p. 313. 

v. Richthofen, Geogn. Besch. von Siid-Tyrol, 1860, p. 146. 

Keibel, Zeitschr. d. d. geol. Ges. 1857, vol. ix. p. 573. 

Koch, Jahrb. d. Ver. f. Naturk. in Nassau, 1858, vol. xiii. p. 123. 

Kjerulf, Christianias Silurbildungen, 1855, p. 23. 

Streny, Zeitschr. d. d. geol. Ges. 1858, vol. x. p. 174; Neues 
Jahrbuch fiir Mineralogie, 1862, pp. 513 and 932, 1864, p. 257. 

Drysdale, London and Edinb. Phil. Journ. 1833, vol. xv. p. 386. 

EMmen, Ann. des Mines, 1847 [4] vol. xii. p. 629. 

Jenzsch has analysed the hypersthenite of Neurode in Silesia, 
which contains bright shining spots and distinct particles of 
chlorophoeite in dark brown-green matrix, and pronounces 
both from chemical and microscopic analyses that the 
matrix consists of about 27 oligoclase and 25 augite, and of 
39 vitreous felspar, 5 magnetic iron-ore, 2 chlorophoeite and 



GREENSTONE GROUP. 153 

2 apatite. He found the content of silica very high, viz. 
66-5. Poggend. Ann. 1855, vol. xcv. p. 418, and v. L. u. 
Br. Jahrb. 1857, p. 436. 

Websky, Gabbro von Neurode. Zeitschr. der deutschen geol. 
Gesellsch. 1864, p. 530. 

6. DIORITE. 

DIORIT. (Germ.) 
DIORITE, Haiiy. (JFV.) 

A crystalline-granular compound of felspar and horn- 
blende. The felspar is not orthoclase. In fresh state 
it is usually dark green. 

Spec, grav . 2'6 2-9 

Contains Silica ...... 47 58 p. c. 

Diorite was first so named by Haiiy. Its texture is 
often so fine-grained that it is difficult to determine the 
species either of its felspar or hornblende, although the 
minute particles of the former in most cases shew the 
fine parallel striae which are characteristic of albite, 
oligoclase, anorthite, or labradorite, and which forbid the 
idea of orthoclase. Gustav Rose in his first work on 
greenstones held the felspar of diorite to be albite. Sub- 
sequently he embraced the view that albite never occurs 
at all in crystalline rocks. Although this latter opinion 
is shared by few, yet all observers now agree that the 
felspar in diorite which was formerly taken for albite is 
usually oligoclase. Delesse again has recognised labra- 
dorite and anorthite as essential ingredients in many 
kinds of diorite. Thus the difference in the species 
of the felspar constitutes one class of varieties of the 
rock. The hornblende is also various : generally it is the 
ordinary hornblende ; sometimes, however, a variety more 
approaching to actinolite, and Breithaupt lately disco- 
vered an entirely new species of hornblende as an essential 
ingredient in many greenstones of Servia, Transylvania, 
and Hungary. It has a black colour and greenish-grey 
streaks. He named it gamsigradite after the name of the 
place where he first found it. 

But inasmuch as it is not easy, and in the fine-grained 
state of the rock impossible with certainty, to recognise 
the different species of felspar and hornblende, it does not 
appear to us desirable on their account to dignify these 
different varieties of diorite with the character of indi- 



154 BASIC IGNEOUS EOCKS. (2) PLUTONIC. 

vidual rocks, although it is well to distinguish them where 
possible, since they are somewhat mineralogically dif- 
ferent. The gamsigradite variety has been named by 
Breithaupt timacite, from one place where it occurs. 
This timacite has also a geological importance, as it is 
found to have broken through the older tertiary strata of 
Hungary and Transylvania, whereas the greater number 
of diorites are much more ancient. 

All these mineralogical differences are very trifling in 
a chemical point of view ; so that we may well consider 
them but as the result of somewhat unequal cooling of 
the same original mass. We do not mean that they 
should therefore be disregarded, on the contrary we 
consider that it would be an inquiry of the greatest 
geological interest to endeavour to trace their causes. 
Such an inquiry, to be successful, however, would demand 
a comparison of many special and accurate observations of 
the rock taken from various localities. 

The following minerals sometimes occur in diorite as 
accessories ; mica (brown and black) pyrites, magnetic 
pyrites, magnetic iron-ore, titaniferous iron-ore, titanite, 
garnet-pistacite, and quartz. Some of these may be of 
secondary origin, e.g. the pyrites and the pistacite, which 
latter appears to have proceeded from the hornblende, and 
sometimes contributes to the green colour of the rock. 

The fine-grained varieties of syenite may be easily 
mistaken for diorite, the only essential difference between 
the two being that orthoclase is a necessary ingredient of 
syenite. The following characteristics may assist in dis- 
tinguishing the two rocks, although not always to be re- 
cognised in them, nor universally to be relied on. Diorite 
is more frequently fine-grained than syenite, and gene- 
rally (owing to its hornblende) more green in colour. In 
diorite the felspar decomposes sooner than the horn- 
blende, and therefore on weathered surfaces the latter 
often protrudes prominently, whereas syenite weathers 
more evenly and falls into a kind of sandy grit. Diorite 
usually contains more pyrites than syenite, and the latter 
more frequently contains titanite or wohlerite than the 
former. Their variations of texture and their outward 
structure, as well as their place in nature, are usually 
somewhat different, as will appear from the short ac- 



GREENSTONE GROUP. 155 

count which we shall give of each under their respective 
heads. 

As varieties of texture without regarding varieties of 
composition, the following kinds of diorite may be distin- 
guished : 

Varieties in Texture. 

(a) GRANULAR DIORITE. \ The most normal variety, e.g. at the 
KORXIGER DIORTT. (Germ.) \ Klumpsen mountain, near Ebers- 

DIORITEGRAMTOIDE. (Fr.) ) 



(6) FINE-GRAINED DIORITE. \ Passing into compact (aphanite) 
FEIXKORXIGER BIS DICHTBR ! Belmsdorf, near Bischofswerda, in 

DIORTT. (Germ.) [ nV^loneU* 

DIOKITK UTHOIDE. (Fr.) ) Oberlausitz. 

(c) PORPHYRITIC DIORITE, or DIORITE- j with crystals of felspar or 

PORPHYRY. I amphibole, going over into 

PORPHYRARTIGER DlORTT. (Germ.) nnhamtif nnmhvrv 

DIORITE PORPHTROIDE. (Fr.) ) a lc P or P n y r y- 

(d) SLATY DIORITE, or DIORITE-SLATE. j The slaty texture usually 

DIORIT-SCHIEFER. (Germ.) [ imperfect, passing into 

DIORITE SCHISTOSE. (Fr.) } apfanite slate. 

(e) ORBICULAR DIORITE, or ] The globular conformation is only 

NAPOLEONITE. ! a local appearance in diorite. It 

(Germ.) f occurs very characteristically and 
1111 ' BrOH9 ~) Beautifully near Sautina and Ajac- 
cio, in Corsica. The rock consists, 
according to Delesse, of a combination of anorthite, blackish- 
green hornblende, and some quartz, so that it is a distinct 
variety in respect of its composition no less than its texture. 
The constituent minerals form alternating concentric layers 
round kernels. The kernels themselves consist (almost exclu- 
sively) either of the anorthite or hornblende (not of both), and 
they likewise exhibit a radiated texture. Thus we find balls 
of from one to three inches in diameter, whose section shews 
rings of alternate light and dark colour. 

At Schemnitz (Stephen-shaft) orbicular timazite occurs, but 
the spherical masses are not in concentric layers. 
(/) AMYGDALOIDAL DIORITE. ) Only occurs rarely, and with 

MAXDELSTEIXARTIGERDIORIT. (Germ.)) a fine-grained to compact 
matrix, which passes into the state of aphanite. 
, O) WACKENITIC DIORITE, or\ This decomposed discoloured, and 
DIORITE-WACKE. L somewhat earthy state can only be 

SSSSStfSfU.) I rg^h certainty as belong- 
ing to dionte by tracing its transi- 

tion from distinct rocks. The foregoing differences of texture 
are however repeated in it. 

Varieties in Composition. 

(A) COMMON DIORITE essentially consisting of oligoclase and horn- 
blende, the diorite of the Huhnberge, in the Thuringian Forest, 
is somewhat differently composed, inasmuch as its felspar con- 
tains lithia, and very many small needles of apatite occur 
disseminated through the whole mass. This rock, which is 



156 BASIC IGNEOUS BOCKS. (2) PLUTOXIC. 

sometimes very coarse-grained, has broken through the rothlie- 

gende and becomes quite compact near the surfaces of contact. 

() AsroRTHiTE-DiORiTE. i In. which the oligoclase is partly or 

AXORTHIT-DIORIT. (Germ.) f wholly replaced by anorthite. As for 

instance in the orbicular diorite of Corsica, which likewise 

contains some quartz. 
(k) TIMAZITE (TRACHTTIC GREENSTONE). } Consists, according to 

TIMAZIT, Breithaupt. (Germ.) ] Breithaupt, of a grey 

or greenish-grey felsitic base, in which are imbedded crystals 
of white felspar (albite or mikrokline), black hornblende (gam- 
sigradite), some mica, magnetic iron-ore, and iron pyrites. The 
base, which is tine-grained to compact, corresponds most closely 
with labradorite. 

The cleavage-prism of gamsigradite shews an angle of 
124 26', its hardness is 7, and spec. grav. is 3 1' ; it has a 
greenish-grey streak. The mica forms hexagonal brown plates. 
The magnetic iron-ore forms very small grains or crystals, 
the iron pyrites very small cubes. 

According to an analysis by Dr. Rube the tirnazite of Gam- 
sigrad, in Servia, contains about 50 per cent, of silica. We 
have already stated that this rock is frequently met with in 
Transylvania and Hungary, especially in the mining districts, 
and that it has penetrated through the Eocene sandstones. We 
have elsewhere described a rock occurring in Borsabanya, in 
the Marmaros, in the north of Hungary, which we named 
labradorite -rock, because its prevailing base consists of labra- 
dorite. According to Breithaupt this is essentially the same 
as timazite j but we find from Dr. Rube's analysis that it con- 
tains above 63 per cent, of silica, and therefore it belongs to 
the acidic rocks. As, according to Delesse, the diorite of Pont 
Jean, in the Vosges Mountains, also contains labradorite, it is 
very possible that it is a timazite. 

(T) CALCAREOUS DIORITE. ) ls the name g iven b 7 Senftto a dark- 
KALK-DIORIT, Senft. (Germ.) \ green, more or less distinct compound 
HEMITHRENE. (Fr.) ) O f hornblende, oligoclase and mica, 

penetrated with calcspar, and which near Ruhla, in the Thurin- 

gian Forest, forms a stratum in mica-schist. 

The jointed structure of the diorites is usually irre- 
gular ; but sometimes columnar or globular. 

Diorite frequently occurs in subordinate masses, veins, 
or dykes in the schistose or slaty rocks of the Silurian or 
Devonian age, and (exceptionally) sometimes in much 
newer formations ; sometimes also in granite, gneiss, or 
mica-schist. 

Appendix. 

The NORITE of Esmark (different from that of Scheerer) very 
widely spread in Norway, appears only to be a variety of 
diorite containing quartz and mica. 

The OPHITE of Palassou is, according to its description, a tolerably 



GREENSTONE GROUP. 157 

compact diorite. The MiCA-DiORiTE of Delesse on the other 
hand ought rather to be classed with Syenite than here, on 
account of its containing orthoclase. 

References. 

G. Rose on Greenstones in Poggend. Annal. 1835, vol. xxxiv. 

p. 1. 
Keibel, Analysen in d. Zeitschr. d. d. geol. Ges. 1857, vol. ix. 

p. 575, and v. Leonhard u. Br. Jahrhuch, 1859, p. 445. 
Riviere, Bullet, de la Soc. ge"ol. d. Fr. 1844, vol. i. p. 528. 
Hunt in Sillim. Amer. Journ. 1859 [2] xxvii. p. 340. 
v. Richthofen, Geogn. Beschreibung v. Siid-Tyrol, 1816, p. 111. 

The diorite at Klausen contains actinolitic hornblende with 

oligoclase. 
Delesse on Orbicular diorite, which was first described in 1785 

bv Besson, in the Journ. d. Phys., and on the Diorite of the 

v osges, Ann. des Mines, 1859, vol. xvi. pp. 160 and 339 : 

1851, p. 149. 
Brctihaupt on Timazite, in the Berg- u. Hiittenm. Zeitg. 1861, 

p. 51. On the Diffusion of Timazite. 

Compare Cotta's Gangstudien, vol. iv. pp. 28, 56, 65, and 85. 
Senft on Calc-diorite. In the Zeitschr. d. d. geol. Ges. 1858, 

p. 308. 
Esmark on Norite in the Magaz. for Naturvidenskabern, vol. i. 

p. 207. 

Charpenticr on Ophite, Constit. g6ol. des Pyrenees, 1823, p. 481. 
Dufrenoy on Ophite, Ann. des Mines, 1832 [3] vol. ii. p. 21. 
v. Rath. The diorite of Neurode, in Silesia, consists of 56 

parts of hornblende, and 44 saussurite. The former has been 

formed from augite according to G. Rose, Pogg. Ann. 1855, 

vol. xcv. p. 655. 
Herm. Vogclgesang, as to globular diorite, Berggeist, 1862, 

Nos. 90 and 91. 

7. APHAKITE. Trap in part, Melaphyre in part. 
APHANIT. (Germ.} 
APHANITE, Hauy. (Fr.) 

A compact, apparently homogeneous mass ; usually dark 
green to black ; of about the hardness of felspar ; 
very tough ; sometimes porphyritic by reason of crys- 
tals of felspar, hornblende, or pyroxene ; also vesicular 
or amygdaloidal. 

Spec, grav 2-62-9 

Contains silica .... 43 58 p. c. 

The separate ingredients of the principal mass of this 
rock are not to be recognised with the naked eye, hence 
the name of aphanite, given by Haiiy. Wehave already 
shown that transitions take place into aphanite from 
diabase, gabbro, or diorite ; proving it to be but a com- 



158 BASIC IGNEOUS ROCKS. (-2) PLUTONIC. 

pact state of one or other of those rocks, bearing the same 
relation to them as basalt to dolerite; a view which is 
entirely confirmed by chemical analysis. 

The minuteness and intimate union of the individual 
constituent ingredients of aphanite when quite compact, 
no less than their general resemblance to each other, 
make it impossible with the ordinary aids to discover 
from the appearance of the rock whether it belongs to 
diabase, gabbro, or diorite. We can only draw conclu- 
sions in this respect from finding it in conjunction with 
one or other of those rocks. If, however, the aphanite 
be porphyritic, then the minerals porphyritically enclosed 
in the compact matrix may give a clue to the composition 
of the latter ; for instance, we frequently find labradorite, 
oligoclase, pyroxene, or hornblende thus porphyritically im- 
bedded in aphanite. It is dangerous, however, to rely too 
implicitly on conclusions so drawn, and on every account, 
therefore, in describing the varieties of aphanite we refrain 
from the attempt to keep up distinctions corresponding 
to the three normal rocks of diabase, gabbro, and diorite. 

Possibly by careful microscopic observations we might 
succeed in determining the special mineral character of 
every aphanite. But such observations are attended with 
considerable labour, and the appliances are not always 
within reach; on a journey they would be out of the 
question. We may, however, state that the microscopic 
observations which have been made of aphanite entirely 
confirm what we have already said respecting its nature, 
and show that even the accessory ingredients of the three 
normal rocks are represented in its composition. The 
greater number of aphanites appear to belong to the 
pyroxenic greenstones, or we might rather say that these 
latter have more frequently assumed the compact state 
than the hornblendic varieties. Many varieties of texture 
and composition which are found in the three granular 
rocks are likewise repeated in the compact rock. 

Varieties in Texture, 
(a) COMMON COMPACT APHANITE. 

GEMEINER DICHTER DIORIT. (Germ.) 

APHANITE LITHOIDE. (Fr.) -VTT-.LT- j. i /i i i ,. T 

(6) PORPHYRITIC APHANITE or With crystals of labradorite, oli- 

APHANITE-PORPHYRY. I goclase, hornblende, augite, or 

PORPHYRARTIGER DIORIT. (Germ.) uralite. Accordingly we dis- 

APHANITE PORPHYROIDE. (Fr.) ) tinguish labradorite - porphyry, 



GREENSTONE GROUP. 159 

oligoclase-porphyry, augite-porphyry, or uralite-porphyry, of 
which we will treat more at large hereafter. 

Near Manebach, Herges, and Tabarz, in the Thuringian 
Forest, there occur aphanitic porphyries whose felspar crystals 
are not yet accurately determined. 

(C> Sl s ATT T ^ PHANITEOrApHiNIIE -) Usually only indistinctly 
AnumttMm. (Otrm.) \ slaty, or of thick cleavage. 

APHANITE scrasrolDE. (Fr.) 

(d) VESICULAR APHANITE. ) Rather rare ; sometimes it would 

BLASIGER APHAXTT. (Germ.) \ appear that the vesicular cavities 
APHANITE VACUOLAIRE. (Fr.) ) have been once filled, and their 
contents weathered out. We often find them empty at the 
weathered surface, but still remaining filled in the fresh in- 
terior of the rock. 

(e) AMYGDALOIDAL APHANITE. -\ The vesicular cavities are most 

APHANIT-MANDELOTEIN. (Germ.) [ usually filled with calcspar or 
APHANITE AMYGDAixtfDE. (Fr.) ) zeo litic substance. 
(/) WACKENITIC APHANITE, orj Discoloured and earthy through 
APHANITE-WACKE. ( decomposition, its petrographic 

APHANIT-WACKE. (Germ.) character only to be determined 
WACKEAPHANITIQUE. (Fr.) ) byitssurrou / dings . 

As varieties of composition the following species may 
be distinguished in addition to the usual quite compact 
form : x 

Varieties in Composition. 

(</) CALCAREOUS APHANITE. ) In the compact and slaty mass are 

KALKAPHANIT, SCHALSTEIN f f oun d n^ing o f calcspar or brown 

] spar which are not fillings up of 

vesicular cavities. 

(A) VARIOLITIC APHANITE, VARIOLITE. ) The compact base con- 

YAIMOI.ITHISCHKH APHANIT,VARIOLTTH. (Germ.) I tains concretions of 
VARIOLJTHE, JADEGLANDULEUX, Brongniart. lie \ 

de Beaumont. (Fr.) > greenish or violet grey- 

ish colour, either of stringy, radiated, or concentric texture from 
the size of a grain of mustard-seed to that of a walnut, firmly 
grown in, and not very sharply defined. They consist of a 
felsite (probably labradorite), but frequently also contain some 
pistacite in concentric layers. As accessories in the matrix of 
the rock we find iron pyrites and magnetic iron-ore, in its clefts 
and cavities quartz, pistacite, calcspar, and chlorite. 

Delesse has narrowly investigated and described the vario- 
lites of the Durance, and he also mentions those of the Fichtel- 
gebirge, and of Savoy, &c. (Ann. des Mines, 1850, vol. xvii. p. 
11(3.) Their spherical concretions often exhibit a reddish, violet, 
or grey kernel, round that a lighter coloured rind, and round the 
latter a green shell of a somewhat lighter colour than the 
enclosing matrix of the rock. In the latter, with the aid of 
the microscope, he also discovered small laminae of felspar. 
(*) LABRADORITE-PORPHYRY(BLACK PORPHYRY).) The black matrix 
LABRADORPORPHYR. (Germ.) [incloses crystals 

MELAl'HYHE fKLD.Sl'ATHiyUE. (Fr.) 1 / i r j S j 

oi laDraciorite and 



160 BASIC IGNEOUS EOCKS. (2) PLUTONIC. 

small particles of a dark green mineral not yet determined ; spec. 
grav. 2-7, content of silica 56-58 p. c. By aid of the magnifying 
glass Streng found the apparently compact matrix to be dis- 
tinctly crystalline, consisting of one mineral of dark-green in- 
clining to black, and another of a lighter green colour. Probably 
they are the same as the minerals which also occur in a distinct 
form. The crystals of labradorite often shew a dark dull-green 
kernel, surrounded by a light and shining margin. The striae 
of twin crystallisation are continued equally through both. 
Sometimes the reverse is the case, the kernel is light and 
shining, and the margin dull and of a darker colour. As acces- 
sories, but rarely, and only in small particles, brownish-black, 
mica plates, pyrites, and magnetic iron-ore. Near Elbingerode 
at the Hartz, this rock penetrates Devonian slates and lime- 
stones. 

To this class belong the rocks described by Delesse, found 
by him at Belfaly and Ternuay, in the Vosges ; these contain 
augite, and are amygdaloidal in part. Also the rock described by 
Kjerulf as melaphyre from Barnekjern, near Christiania, as well 
as many other so-called melaphyres and porfido-verde-antico. 

Streng in v. L. u. Br. Jahrb. 1860, p. 397. 

Delesse in Ann. des Mines, 1847 [4] vol. xii. p. 228. 

Kjerulf, Christiania Silurbecken, 1855, p. 28. 

(&) OLIGOCLASE-PORPHYRY. \ Is the name given by G. Eose to a 
OLIGOKLASPORPHYK. (Germ.) J diabasic or aphanitic rock in the Ural 
Mountains, which has a dark green compact or nearly compact 
matrix containing crystals of oligoclase. Much porfido-verde- 
antico is of this character ; also the rock described by Delesse, 
as found by him at Lescines, in Belgium, containing some 
pyrites, and some copper pyrites (unless it belongs to mica- 
diorite) and several rocks from the neighbourhood of Christiania 
described by Kjerulf. 

G. Rose, Keise nach dem Ural, vol. ii. p. 571. 
Delesse. Bulletin de la Soc. geol. d. Fr. 1849 [2] vol. vi. p. 
386 ; 1850 [2] vol. vii. p. 310. 

) Christiania Silurbecken, 1855, p. 9. 



ATJGITE-PORPHYRY. | (Often called Melaphyre,) A com- 

AUGITPORPHYR. (Germ.) \ p ac t matrix, usually dark green, 

MELAPHYRE PYROXENIQUE. (Fr.) ) Containin c ' rsta ls of auite! 



Fr. v. Richthofen reckons to this division the most of the 
rocks of the Fassa region, which are usually designated as 
melaphyres. 

These contain crystals of augite and labradorite (or sometimes 
oligoclase), inclosed in a matrix resembling basalt. Titaniferous 
iron-ore is also disseminated through the mass in small par- 
ticles. They are very variously developed ; most frequently we 
find them vesicular and amygdaloidal. 

V. Richthofen, Southern Tyrol, 1860, p. 128. 

(jri) URALITE-PORPHYRY. \ Is the name given by G. Rose to 
URALITPORPHYR,^. Rose. (Germ.) \ rO ck containing crystals of uralite 
PORPHYRE 1 OURALITE. (Fr.) ) ^ ft CQmpact dark; pro bably diabasic 



GREENSTONE GROUP. 161 

matrix. This uralite has the form of augite, and the substance 
of hornblende. 

G. Rose, Reise nach dem Ural, vol. ii. p. 370. 

The four last-named varieties may be indifferently 
termed aphanitic porphyries, or greenstone-porphyries ; 
and they are sometimes classed together under the name 
of melaphyres. The timazites of Hungary likewise fre- 
quently have a compact aphanitic base, for instance, those 
in the neighbourhood of Schemnitz, in which single crys- 
tals or crystalline particles of hornblende (gamsigradite) 
or felspar may be clearly distinguished. 

Aphanite is usually of jointed structure, or very dis- 
tinctly cleft.; generally the blocks are irregularly massive, 
sometimes, however, regularly columnar, or regularly or 
irregularly spherical. The aphanites occur in nature under 
the same circumstances as diabase, diorite, and gabbro ; 
and very often in their company. We have already sug- 
gested that they should be regarded as mere modifications 
of those rocks, differing from them chiefly in the greater 
rapidity of their original cooling process. The Saxon 
Oberlausitz affords striking instances in illustration of this 
opinion. The granite region there is found to have been 
broken through by diorite, and accordingly numerous 
dome-shaped hills of the latter rock protrude from the 
surface ; near to these the same eruptive mass has pro- 
duced narrower dykes (from 5 to 20 ft. thick), whose 
texture is fine-grained, nearly compact. Near Belmsdorf, 
not far from Bischofswerde, we observed a diorite dyke 
20 to 30 ft. thick, which in the centre was fine-grained, 
but almost compact towards the walls of the cleft, where 
it must have cooled more quickly. The offshoots from the 
same vein into the granite, and the narrow parts of the 
principal vein of only two inches thick, consist of a com- 
pletely compact mass, which might easily be taken for 
basalt, as it is almost quite black. These differences of 
texture are there manifestly the consequence of different 
degrees of rapidity of cooling caused by the different 
volume or thickness of the mass. 

On this subject see Erlauter. z. geog. Karte von Sachsen, 1839. 

No. 3, p. 24. Also on the subject of aphanitc, 
Dclesse in Ann. des Mines, vol. xvi. p. 350. 

M 



162 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

8. MELAPHYRE. Augite-Porphyry in part, Trap in 

part. 

MELAPHYB. (Germ.') 
MELAPHYHE, Brongniart. (Fr.) 

The rocks which we include under this name are dark- 
coloured, greenish, brownish, or black ; compact, por- 
phyritic, vesicular, or amygdaloidal ; always free from 
quartz. They are compounds (intimately blended) of 
felsite, pyroxene, hornblende, and magnetic iron-ore. 

Spec. grav. 2'6 3-1 

Contains silica ..... 54 62 p. c. 

The name melaphyre has ceased to bear a distinct 
character, having been successively used by different 
geologists, ever since the time of Brongniart, who first 
introduced it, for many and various igneous rocks having 
nothing in common with each other, unless it be a pre- 
valent compact texture, dark colour, and absence of 
quartz. Hence the name conveys no definite idea, unless 
qualified by the name of a particular author, and that is 
not always sufficient without the name of the locality. 

There are many and various rocks of uniform dark 
colour, of a prevailing compact or amygdaloidal texture, 
close compounds of some kind of felspar with pyroxene, 
hornblende, and magnetic iron. We have already 
spoken of several such under the heads of basalt and 
aphanite. Much of what has been called melaphyre cer- 
tainly belongs to our basalts and greenstones. The rocks 
of which we shall treat under the name of porphyrite 
have often been called melaphyre, and if we take away 
all that may be ascribed to basalt, greenstone, and por- 
phyrite, little will be left to which to apply the name of 
melaphyre. 

Under these circumstances the name can only be use- 
fully retained as a sort of provisional term for any basic 
igneous rocks of prevalent compact texture and dark 
colour, whose composition is not so definitely marked as 
to entitle them to be included under any other more 
distinct species ; much in the same way as we are often 
compelled to use the general name of greenstone for 
rocks whose mineral character is not sufficiently decided, 
or has not been sufficiently investigated, to enable us to 
class them as diorite, gabbro, or diabase. 



MELAPHYRE. 163 

In dealing thus, for our own part, with the name of 
melaphyre, we here subjoin a quasi-historical account of 
the mode in which it has been used by different authors. 
\Ve think the divergence of their readings will be a 
sufficient justification, if any be needed, for the way in 
which we propose that the term should in future be 
accepted. 

(a) Al. Branrjniart, the inventor of the name melaphyre, described it 

as l Pate noire d'aniphibole pe"trosiliceux enveloppant des 
cristaux de feldspath ; ' what is here meant by 'amphibole pe"tro- 
siliceux ' is very uncertain, the more so as at that time (1813) 
the differences Between hornblende and pyroxene were not so 
well established or known as they are at present. 

(b) L. von Bttch lirst applied Brongniart's name of melaphyre to 

certain black-coloured rocks of the Fassa Thai and the Seisser 
Alp (see ante, p. 162). He, however, also called these rocks 
black porphyries or augitic porphyries, because they contained 
crystals of augite, and their matrix was also black and rich in 
augite. He also included under the same designation many 
rocks of the Hartz and Thuringian Forest, &c., whose compo- 
sition he presumed to be similar, and which he considered to be 
the original cause of the upheaval of those mountains. To 
them he also ascribed the formation of dolomite in several 
localities. As the principal characteristics of this rock, he 
enumerated dark colour, great content of augite, and complete 
absence of quartz. See von Leonhard's Taschenbuch, 1824, 
vol. ii. pp. 289, 372, 437, and 471. 

(c) Xatnnann says on this subject, ' The rocks which Al. Brong- 

niart has introduced under the somewhat singular name of 
melaphyre are for the most part identical with those which 
Faujas de Saint Fond collected under the Swedish name of 
trap, and of which Warmholz, Steiniger and others have 
made use in the same sense. Werner called them trap-por- 
phyries or trap-amygdaloids ; Zobel and v. Carnal, porphy- 
rite. Freiesleben called them pseudo-porphyries ; v. Raumer, 
basaltite ; and in many French writings they ara also in part 
called spilite. Trap and melaphyre are probably the most usual 
names at the present day ; for although the Swedish trap, ac- 
cording to Erdrnann is a diabasic rock, whereas the rocks 
which bear the same name in the Faroe Islands and Iceland 
are basaltic formations, it nevertheless appears to be most useful 
to retain (with L. von Buch) the name of melaphyre for the 
rocks which we are about to treat.' These are tnen described 
as compounds of labradorite, and (probably) augite in small or 
invisible crystals (therefore compact), but alone recognisable, 
and frequently in the form of scattered crystals, the rock very 
much inclinecl to the amygdaloidal in 'texture. They are 
further described as always containing magnetic iron-ore, car- 
bonate of protoxide of iron, and carbonate of lime, in invisible 
particles, as well ns some rubellan and mica. Their petro- 

H 2 



164 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

graphic difference from the basalts, according to Naumann, is 
confined to the want of olivine, and to the circumstance that 
the augite is not to be recognised with certainty. Geognosie, 
and in v. L. u. Br. Jahrb. 1860, p. 1. 

(0) Von Richthofen attempted to put an end to the confusion 
which the name of melaphyre had gradually introduced by 
restoring the definition of Brongniart, and he believed that he 
had discovered the identical rock in various places ; for instance, 
at Schneidemiillersberg near Ilmenau, in the Schleusenthal, in 
the Thuringian Forest, between Landshut and Glatz in Silesia, 
near Oberstein, and between Botzen and Colmann in the Tyrol. 
He describes the rock thus : 

Compact matrix, dark-green or brown to black. Fracture 
uneven, inclining to conchoidal ; lustre shining ; hardness that 
of felspar or less; spec. grav. 2*7; contains crystals of felspar 
(oligoclase or labradorite), other minerals only exceptionally to 
be recognised. In his large work on the Tyrol he also reckons 
the rock of which the summit of the Margola is formed to this 
compound of oligoclase and hornblende, with much oligoclase, 
labradorite, augite, and hornblende, and partly of a fine-grained 
species ; it consists partly of an intimate compound of oligoclase, 
and few crystals of augite. This latter variety was termed by 
v. Klipstein mulatt-porphyr. 

From the results of the chemical and microscopic analyses 
of these rocks, from the minerals which they contain in a dis- 
tinctly crystalline form, and from their specific gravity, von 
Richthofen framed conclusions respecting the mineralogical 
composition of the compact matrix, and pronounced it to con- 
sist essentially of oligoclase and hornblende, with subordinate 
quantities of apatite, titaniferous iron, sometimes also some 
magnetic iron-ore, and chlorophseite, or magnesia-mica. In it 
often labradorite crystals lie imbedded exceptionally, perhaps, 
also similar ones of augite, hornblende, epidote, or mica, but 
never quartz or olivine. 

In vesicular cavities there occur quartz and chalcedony, car- 
bonic spars and zeolites. (Vide Zeitschr. d. d. geol. Ges. 1856, 
pp. 589 and 593, which gives a very complete catalogue of the 
literature on this subject; Sitzungsb. d. Wiener .Akad. d. 
Wissensch. 1857, vol. xxvii. p. 293 ; Remarks upon the dis- 
tinctions between melaphyre and augite-porphyrj^, Vienna, 
1839, and Geogn. Beschreibung v. Siid-Tyrol, I860. p. 141.) 
(e) E. Sochtinff, on the other hand, attempts to show that Richt- 
hofen's definition of the matrix is unfounded ; that accord- 
ing to the results of the analyses, it might just as well consist 
of labradorite and augite, and that Brongniart was not to be 
depended upon as to the determination of hornblende (Zeitschr. 
d. d. geol. Ges. 1857, p. 427). Sb'chting himself had formerly 
described the so-called melaphyres of the Thuringian Forest as 
an intimate compound of labradorite and augite in the Zeitschr. 
d. ges. Naturwissenschaften, 1854, p. 197. 

(/) Girard starts with the principle that the geological character of 
rocks is the principal thing to be determined, and that they 



MELAPHYRE. 165 

should always be classed and named accordingly, rather than 
according to their mineralogical or chemical composition. He 
combats von Richthofen's view in respect of melaphyre, but 
seems somewhat to have misunderstood his meaning. For 
Richthofen merely sought to avoid the uncertainty into which 
the term melaphyre had fallen by keeping as strictly as possible 
to Brongniavt s first definition, and thereby excluding many 
rocks which had been called melaphyres. Girard, on the other 
hand, seeks to show that many of these excluded rocks really 
contain augite and no hornblende, a fact not disputed by 
Richthofen, but one which according to him did not entitle 
them to be called melaphyres. We may, perhaps, think von 
Richthofen's narrowing of the sense of melaphyre impractical 
or inconsistent : unpractical because, being too much opposed 
to prevailing ideas, it is little likely to be adopted ; inconsistent 
if taken in connection with the enlargement of the meaning of 
the term trachyte which he himself advocated. Nevertheless 
it does not follow that it is in itself inaccurate, even if we 
choose to acknowledge Girard's premised principle to be the 
ri^ht one. Girard himself considers the melaphyre of Ilfeld 
to be a compound of a mineral containing felspar with augite, 
the augite forming only one-fifth or one-sixth of the entire 
mass. Whether the prevailing ingredient be labradorite or 
oligoclase, he leaves undetermined. Small black grains in the 
same mass, he takes for magnetic or titaniferous iron. He 
compares also some other .melaphyre with that of Ilfeld. 
(v. L. u. Br. Jahrb. 1858, p. 173.) 

(g) Streny distinguishes three kinds of rock in the neighbourhood of 
Ilfeld by the names of melaphyre, porphyry-melaphyre, and 
melaphyre-amygdaloid. The first, which should belong to our 
porphyrite, is a grey or brown-coloured rock with matrix re- 
sembling hornstone, and containing small crystals of felspar 
not longer than the tenth part of an inch, white or greenish 
with twin strise (labradorite or oligoclase) associated some- 
times with crystals of an undetermined dark-green mineral 
grown into the felspar crystals ; the matrix likewise contains 
small reddish-brown garnet grains, also a light-green mineral, 
perhaps only the product of decomposition and very small par- 
ticles of magnetic iron-ore. 

In the melaphyre of Streng the principal mass is of dull ap- 
pearance, a'nd in its fresh state is blue-black, distinctly crystal- 
line, of wavy lustre and friable by weathering it becomes 
greenish-grey or brown. It is probably a compound of felsite 
and augite or hornblende, or a yet undefined mineral of the 
nature of diallage and some magnetic iron-ore. In the matrix 
occur very small crystals of the same diallage-like mineral, also 
hirircr columns of the same mineral which exhibit a growth of 
t win crystals, crossing each other regularly at an angle of 60, 
and distinct small plates of rubellan. In a second essay Streng 
described the diallage-like mineral as a schillerspar which con- 
tains alumina. 

The melaphyre-amygdaloid of Streng consists of a homo- 



1G6 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

geneous brown matrix, of the hardness of 5-6, and contains 
small amygdaloidal cavities filled with glauconite, chalcedony, 
and carbonate of lime. 

The specific gravity of these varieties fluctuates between 2 '6 
and 2-7. Their content of silica, taking the mean of a consider- 
able number of analyses, is for the melaphyre-porphyry 61'3, for 
the melaphyre and melaphyre-amygdaloid 54'4. They form 
together a plateau of considerable size between the lower and 
upper Rothliegende districts (Zeitschr. d. d. geol. Ges. 1858, 
p. 99, and 1859, p. 78). Upon the position and bedding of these 
rocks see Bantsch in Abhandl. d. naturf. Ges. zu Halle, 1858. 
(h} G. Hose defined the Ilfeld melaphyre as follows : a fine-grained 
almost compact mass of black or brown colour, sometimes con- 
taining small acicular crystals, or greenish-white crystals, 
(likewise small). The texture is often vesicular or amygda- 
loidal. According to the known analyses, both microscopic and 
chemical, the matrix most probably consists of an intimately 
blended crystalline compound of oligoclase, with augite or 
hornblende, magnetic iron-ore, and some apatite; the fine 
acicular crystals appear to be augite transformed into schil- 
lerspar; the greenish white crystals Rose could not determine. 
In local varieties also small crystals of mica occur and irregu- 
larly shaped grains of some other mineral. 

The vesicular cavities, often very regularly shaped (for in- 
stance pearshaped), contain concentric layers of chalcedony and 
quartz as well as calcspar. 

The following are varieties more especially distinguished by 
Rose. 

Black melaphyre, from the Raben Klippen, at the Hartz. A 
compact compound in which transparent prismatic crystals are 
prevalent ; between them lie larger white crystals, very small 
grains of magnetic iron-ore. 

Black melaphyre from Wieprersdorff. Matrix under the mi- 
croscope less distinct than the last-named ; in it lie diallage-like 
crystals of augite. 

Red melaphyre from Wiegersdorff. Matrix under the mi- 
croscope less distinct than the last-named; in it lie diallage- 
like crystals of augite. 

Red melaphyre from the Birkenhoff. The matrix reddish- 
brown, and containing green acicular crystals of augite. 

Ro^e considers these melaphyres to resemble chiefly those of 
Lowenberg, Lahn, and Landshut in Silesia. (Zeitschr. d. d. 
geol. Gesellsch. 1859, p. 280.) 

(f) THE OBERSTEIN AMYGDALOID. This rock, celebrated for its 
beautiful agates, is considered by many geologists to belong to 
the melaphyres ; thus (e. g.) : von Dechen, Dufrenoy, Elie de 
Beaumont, and Naumann. Its principal mass, usually brown or 
greenish, no doubt consists chiefly of felsite, and often contains 
small crystals of felspar, and amygdaloidal cavities filled with 
agate and other minerals ; accordingly we should term the rock 
a porphyrite. Delesse was the first to give a careful analysis 
of it. Its spec. grav. is 2-68. Chemically it contains 51-13 



MELAPHYRE. 167 

silica, 29-73 alumina and peroxide of iron, 473 of lime, 4073 
magnesia and alkali, 3*68 water and carbonic acid. From these 
data, as well as its mineralogical characteristics, Delesse con- 
cludes that the principa. mass essentially consists of labra- 
dorite ; in fact, there frequently occur in it a great number of 
small labradorite crystals, white and translucent : its frequent 
green colour appears to be owing to an admixture of chlorite. 
Sometimes some aueite is observable, also small flakes of 
brown mica. Magnetic iron-ore in very finely divided particles 
appears to be uniformly dispersed through the whole mass. 

In the numerous amygdaloidal cavities, whose diameters 
vary from one-tenth of an inch to a foot, Delesse found agate, 
opal, quartz, chlorite, calcspar, different kinds of zeolite, hy- 
drated oxides of iron and manganese. 

The amygdaloid of Oberstein possesses compact fine-grained 
and porphyritic varieties, and occurs in the coal formation of 
that district, sometimes forming dykes and masses of consider- 
able size, sometimes parallel seams. It appears to have been 
t lirust up about the time when the deposit of the rothliegende 
began. Perhaps its character is the same as that of the rock, 
previously described under the name of tholeite. (See ante, 
p. 138.) 

(Delesse in Ann. des Mines, [4] vol. xvi. p. 511 ; Steininger, 
Geogn. Beschreib. d. Landes. zu Saar. u. Rhein, 1840, p. 110.) 
(k) Senft designates as melaphyres almost all dark quartzless igneous 
rocks of the Thuringian Forest ; according to him, they consist 
principally of a compact mass of labradorite, combined with 
in;i<rnetic titaniferous iron-ore, calcspar, ironspar, and iron- 
chlorite (delessite). He distinguishes several varieties, viz. : 
in the first place, those resembling greenstones from those 
resembling basalt or felsite-porphyry, then according to their 
texture; (1) granular like dolerite, near Schmiedelfeld ; (2) 
porphyritic (melaporphyry), which he subdivides into labra- 
dorite- and melaphyre- (trap-porphyry), mica-porphyry and 
iron-chlorite (delessite) porphyry ; (3) nielaphyre-amygdaloids, 
and (4) compact or fine-grained melaphyres. "Surely these are 
rocks of very various character. 

(Bericht der Naturforscherversammlung zu Wien, 1858, 
p. 144.) 

As regards the so-called spilites of the Western Alps, which 
ore also considered to belong to the melaphyre, compare 

Gueymard, in the Ann. des Mines, 1850, [4] vol. xviii. p. 54, 
with 

Delesse, ibid. 1857, [5] vol. xii. p. 457. 

E. E. Schnrid on Melaphyre of Mombachler Hofen, between 
Baumholde and Grumbach in Rheinpfalz, in Pogg. Ann. 1863, 
vol. cxix. p. 138. 

Modeling, Melaphyre des Riesengebirges, Neues Jahrb. f. 
Miner. 18G5, p. 344. 



168 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 



PORPHYRITES. 

As the rocks which come under this head are all inti- 
mately connected with each other by transition states, 
and they likewise all assume the same geological position, 
we shall characterise them as the varieties only of one 
species, describing them, nevertheless, individually. 

9. PORPHYRITE. Felspar-Porphyry, Quartzless 
Porphyries, Mica-Porphyry or Hornblende-Porphyry. 

PORPHYRIT, G. Rose. {Germ.} 
POKPHYRITE. {Fr.} 

Contains in a felsitic matrix (usually of dark colour) 
individual crystals of felspar, mica, or hornblende. 
The matrix is sometimes also vesicular or amygda- 
loidal. 

Spec. grav. i - .... 2-627 
Contains silica 59 61 p. c. 

The term porphyry, without addition or qualification, 
denotes, par excellence, quartz-porphyry, a rock with 

Suartz-felsitic base and crystals of felspar and quartz 
see p. 214 post, where it is more particularly de- 
scribed). Naumann, therefore, proposed ^n his treatise 
on Ilfeld) to collect all the quartzless porphyries with 
prevailing felsitic base under the common name of POR- 
PHYRITE, which had already been applied to some of 
them. This nomenclature has now been pretty generally 
accepted. It appears to us certainly better than Rose's 
proposal to designate a part of these quartzless rocks 
syenitic porphyry (see also post, p. 210, where Rose's 
divisions are further explained). Many varieties of por- 
phyrite stand on the very margin between the basic and 
acidic rocks (their silica ranging from 49 to 61 per cent.), 
but the greater part are basic. Quartz only occurs very 
exceptionally in their composition. 

These rocks, by reason of their prevailing dark colour 
and their deficiency in quartz, were formerly frequently 
classed as melaphyres. We have already expressed 
the opinion that most of the so-called melaphyres are 
either basalts, greenstones, or porphyrites, so that there 
is scarcely anything left to which to apply the name of 
melaphyre distinctively. But as it is often very difficult 



PORPHYRITE GROUP. 1G9 

to determine whether a rock is properly a basalt, a green- 
stone, or a porphyrite, the name of melaphyre for such 
doubtful rocks may prove convenient and useful. It might 
have been more correct to give up the name of porphyrite 
and use that of melaphyre in its stead, both because the 
name of porphyrite refers to a texture which is not an es- 
sential feature of these rocks, and because the porphyrites 
are not always in fact porphyritic. Such an innovation, 
which Senft seems really to have intended, was, however, 
open to the serious objection that the name of melaphyre 
had already been so much abused as to make it hopeless to 
attempt now to clothe it with a definite meaning, although 
it may perhaps be usefully retained for rocks of indefinite 
character. 

The porphyrites may be divided into distinguishable 
varieties, according to their different composition. They 
may be best classed according to the distinct minerals 
which occur in them porphyritically. Thus we shall dis- 
tinguish Porphyrite (proper), with crystals of felspar ; 
Hornblende-porphyrite, with crystals of felspar and horn- 
blende ; and Mica-porphyrite, wdth crystals of felspar and 
mica. 

The porphyrites are usually severed by joints into irre- 
gular masses, or very deeply cleft by fissures ; they are 
more rarely jointed in columnar or tabular form. 

In Germany they are not met with of much more re- 
cent origin than the Rothliegende ; this formation is, how- 
ever, sometimes found pierced by them, and the two are 
very often contemporaneous. In Southern Tyrol, much 
more recent porphyrites would appear to occur. 

The porphyrites never occupy connected fields of great 
extent, and in general they are far less widely spread than 
the quartz-porphyries. 

(A) PORPHYRITE (FELSPAR-PORPHYRY). 

PORPHYRIT. {Germ.) 
PORPHYRITE. (Fr.) 

A felsitic principal mass, usually dark-brovm, containing cry stain 
of felspar, oliyoclase, or sometimes orthoclase, and occasionally 
other minerals. 

Spec, grav ' . . 2-6 27 

Content of silica at Ilfeld on the average "| A1 Q 

(therefore very high). . . J 



170 BASIC IGNEOUS EOCKS. (2) PLUTONIC. 

The colour of the matrix varies sometimes into grey, red, 
violet, or blue, and besides the crystals of felspar, it contains as 
accessory ingredients an admixture of garnet, titanite, mag- 
netic iron-ore, specular iron, and pyrites, &c. This porphyrite 
is extensively developed in the South of Norway, where 
L. von Buch has in part named it ' Rhombenporphyr,' on 
account of the rhombic section of its felspar crystals. At 
Elfdalen, in Sweden, it is manufactured into small ornaments. 
It is also very prevalent in the Lenne-Gebiet in Westphalia, 
and on the southern border of the Hartz Mountains. As the 
rock of the last-named locality has been recently very ac- 
curately described, we subjoin a short abstract of those de- 
scriptions. 

Porphyrite (Streng's melaphyre-porphyry, p. 165), found at 
Ilfeld, near the Hartz Mountains, contains in a dark-brown or 
grey felsitic matrix, cry stals of felspar, also a dark-green mineral, 
a light-green mineral, red garnet, and small scales of mica- 
ceous iron. The matrix, according to Streng, consists chiefly 
of orthoclase, which Rose, however, doubts. 

Rose made a microscopic analysis of this rock. The thin 
polished plates showed a transparent matrix marked with black 
spots and streaks, and filled with black grains of irregular 
shape. According to Streng, the felspar crystals as well as the 
grains consist of labradorite. Baentsch and Girard hold the 
dark-green mineral for augite ; Rose, on the other hand, con- 
siders it to be a product of decomposition of hornblende. Ac- 
cording to Streng, black and shining grains of titaniferous iron- 
ore may be recognised in the weathered state of the rock. At 
Ilfeld no vesicular or amygdaloidal varieties of this rock appear 
to occur, unless we regard those amygdaloids as such which 
have been described as melaphyre a view which Streng and 
Naumann disapprove. 

This rock is often of columnar jointed structure; it forms an 
extensive plateau in the region of the Rothliegende, where it 
also probably ramifies downwards in the form of veins. 

Many other porphyrites bear a close resemblance to the 
Ilfeld rock ; for instance : the porphyrite of Korgon in the 
Altai Mountains, which contains greyish-white laminae of 
oligoclase and specular-iron in a reddish-brown matrix ; the 
porphyry of Hainersreuth in the Fichtelgebirge, which has 
reddish-white crystals of oligoclase, and very little specular 
iron in a reddish-brown matrix ; the porphyrite of the Pentland 
Hills, near Edinburgh, with crystals of oligoclase, and specular- 
iron sparkling in a brownish-red matrix ; the porphyrite of 
Ziegenriicken, near Hohenelbe, with crystals of oligoclase, is 
a dark-coloured matrix, and the porphyrite of Rovigo, near 
Lugano, also with oligoclase crystals in a dark matrix. The 
amygdaloids of Oberstein, which we have previously described 
on Delesse's authority, probably also may belong to this class. 

Von Richthofen describes certain porphyritic rocks of Mu- 
latto and Cavalessi, in Southern Tyrol, which contain tabular 
crystals of felspar in a compact, and for the most part reddish 



PORPIIYRITE GROUP. 171 

matrix, or which sometimes consist of a fine-grained mass 
without crystals; others contain liebenerite in the forms of 
nepheline or orthoclase (pseudomorphous) ; these last-named 
rocks form narrow veins, penetrating all the other rocks of that 
district. 

Varieties in Texture. 

( a } PORFHYRITIC. 

(b) COMPACT. 

(') AMYGDALOIDAL PORPHYRITE or AMYGDALOID. 
(d) PORPHYRITE-WACKE. I Somewhat decomposed. AtMa- 

ARGILOPHYRE, Brongniart. (Fr.) J rienberg in Saxony, these veins 
of wacke" in the gneiss rock are called ' Kalchgange.' 

References. 

Strenrj, Zeitschr. d. d. geol. Ges. 1858, p. 106; 1861. p. 87. 

G. Rose, ibid. 1859, p. 296. 

Naumann in v. L. u. Br. Jahrb. 1860, p. 24. 

Girard, ibid. 1858, p. 145. 

JSaentsch, Die Melaphyre des Harzes, 1 858. 

Von RiMofenj Geogn. Beschr. v. Sud-Tyrol, 1860, p. 149. 

Kjemlf, Christiania Silurbecken, 1855, p. 29. The rhomben- 
porphyr of the Vetta Collen (Kjerulf s melaphyr) contains 
large crystals of labradorite in a felsitic matrix, which ac- 
cording to him also contains augite. 

(B) HORNBLENDE-PORPHYRITE. 

HORNBLENDEPORFHYRIT. (Germ.) 

PORPHYRE SYENITIQTJE. (Fr.) 

In a compact felsitic matrix , usually of dark colour, are con- 
tahtt'il cn/xfals or crystalline particles of hornblende and felspar 
(oligoclaae). 

Spec, grav 2-6 2-7 

Contains silica (at Potschappel, near Dresden) 59 p. c. 

The matrix of this rock usually much preponderates over 
the porphyritic crystalline parts, and is in its fresh state usually 
brown, violet-brown, or grey ; becomes lighter in weathering. 

The hornblende forms small columnar or acicular crystals, 
which become very distinct when the matrix is somewhat 
weathered or discoloured. The crystals or grains of felspar 
(oligoclase ?) are often very intimately blended with the matrix, 
and their species is therefore difficult to determine. At Wils- 
(IrutK, in Saxony, and in some other localities, some dark- 
coloured mica occurs, together with the hornblende, forming 
transitions into mica-porphyrite. The rock contains no quartz. 
The matrix is sometimes vesicular or amygdaloidal. Didey 
describes a blue porphyry (probably belonging to this class), 
and occurring at Chaux, near Trejus, where it passes through 
the Variegated Sandstone. He states that it contains crystals 
of hornblende and albite. 



172 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 

This rock is not known to be very extensively developed 
anywhere. In the Plauenschen-Grund, near Dresden, it occurs 
in the neighbourhood of syenite ,- it may possibly represent a 
more compact state of that rock. It is older in that place than 
the coal formation, and even the lower strata of that formation 
contain fragments of it; its jointings show smooth surfaces. 
The masses are irregular, approaching somewhat to the colum- 
nar form. 

To this rock belong many antique porphyries, particularly 
the porfido-rosso-antico, which contains white felspar and black 
acicular crystals of hornblende, and usually some micaceous 
iron in a red matrix. 

A rock occurring at the Hutberg, near Weisig, to the east 
of Dresden (called by Jenzsch ' amygdalophyre '), seems to 
belong here, as it contains some hornblende ; in any case it 
belongs to the porphyrite group. It is often amygdaloidal, 
and contains in its vesicular cavities hornstone, chloraphseite, 
chalcedony, quartz, pyrites, and sometimes felspar, resembling 
petalite, which Jenzsch has called weissigite. 

Varieties of Texture. 

(a) PORPHYRITIC. 

(b) COMPACT. 

(c) AMYGDALOIDAL. 

(d) WACKENITIC. 

References. 

Delesse on the antique red porphyries, Bullet, geol. 1850, 
p. 532 ; also, in v. L. u. Br. Jahrbuch, 1851, p. 422. 

Jenzsch in v. L. u. Br. Jahrb. 1853, p. 386, and in 1854, p. 400. 

Naumann, Erlauter. zur geogn. Karte v. Sachsen, 1845, No. 5, 
p. 202, 

Diday, Ann. des Mines, e*d. 2, p. 193, von L. u. Br. Jahrb. 1855, 
p. 784. 

(C.) . MlCA-PORPHYRITE Or MlCACEOTJS PORPHYRY. 

GLIMMERPORPHYRIT. (Germ.} 

PORPHYRE MlCACE. (Fr.) 

A compact felsitic matrix, usually of dark colour, containing 
crystals or crystalline particles of mica and felspar. 

Spec. grav. ..... 2-62-8 

Contains silica at Meissen . , . 59 p. c. 

The felsitic matrix when fresh is of a brown or violet-brown 
colour, but is lighter when weathered. It incloses distinct 
laminae of mica of dark colour, and often of hexagonal form ; 
also grains or crystals of felspar, sometimes frequently, some- 
times sparingly disseminated. 

The felspar appears to be partly oligoclase, partly orthoclase ; 
it is white, greenish, or reddish j sometimes only in thin 



MICA-TRAP ROCKS. 173 

laminae. Occasionally hornblende or quartz occurs, developed 
in distinct crystals ; and thus a transition arises into horn- 
blende-porphyrite, or granite-porphyry. 

Vesicular and amygdaloidal textures sometimes occur, in 
which case there are usually fewer crystals porphyritically 
imbedded. The amygdaloidal cavities contain green-earth, 
calcspar, and siliceous minerals. 

Mica-porphyrite abounds in the Thuringian Forest, where it 
is usually of irregular massive structure, with perhaps a ten- 
dency to columnar jointing. When it occurs with quartz-por- 
phyry in that locality, it is older than it, and older too than 
the Rothliegende, the conglomerates of which formation contain 
many fragments of mica-porphyrite. Near Meissen a very cha- 
racteristic mica-porphyrite is found penetrating the syenite- 
granite, as well as the granite dykes contained in that rock. 
The veins of the porphyrite are usually compact without 
crystals towards their outward edges, or throughout the vein, 
where the ramifications are narrow. At Zwickau, in Saxony, 
amygdaloidal varieties occur in conjunction with the compact. 

Varieties in Texture. 

(a) PORPHYRITIC. 

(b) COMPACT. 

(c) AMYGDALOID. 

(d) WACK& 

Vide Cotta in v. L. u. Br. Jahrbuch, 1845 ; p. 75. 

MICA-TRAP ROCKS. 

The name mica-trap originated with Naumann, who 
first proposed it for certain rocks of the Erzgebirge, being 
compounds of mica and felspar, but himself afterwards 
(in his ( Geognosie ') preferred the French name of mi- 
nette for the same rocks, which no doubt is their older 
designation. Under these circumstances, it may be ad- 
missible to transfer the name of mica-trap to an entire 
group of similar rocks, whose common attributes are : 
that they consist principally of compounds of mica and 
felspar, without marked porphyritic texture ; and that they 
contain no quartz, unless quite exceptionally. 

We count in this group the following rocks (although 
it is uncertain if they are all of igneous origin), viz. 
Minette, Faidronite, Kersanton, and Kersantite. Until 
that question is determined in the negative, they may be 
so classed on account of their petrographic affinity ; and 
for the same reason they will be most conveniently treated 
as varieties of the same rock. 



174 BASIC IGNEOUS EOCKS. (2) PLUTONIC. 

10. MICA-TRAP. 

GLIMMERTRAPP. (Germ.) 
TRAPP MICACE. (Fr.) 

A compound of felspar and mica. 

Spec, pav 2-5 2-9 

Contains silica .... 50 65 p. c. 

Varieties. 

(A) MINETTE. 

MDTETIE. (Germ.) 
MUSETTE. (Fr.) 

Afelsitic matrix containing much mica and sometimes distinct 
crystals of orthoclase or hornblende ; grey colour predominates. 

Spec, grav 2-5 2-9 

Contains silica ... 60 65 p. c. 

The blackish-brown magnesian mica sometimes predominates 
so completely as to be alone distinctly visible. As accessories, 
there occur hornblende, and sometimes chlorite and magnetic 
iron-ore. Calcspar and sparry iron are probably only of 
secondary origin, and quartz is probably never present. It is 
sometimes difficult to distinguish minette from mica-porphyry 
or from kersantite. 

It is found in considerable extent near Framont, in the Vosges 
Mountains, where it first received its name from the miners, a 
name which Voltz first introduced into science. Near Oederan, 
in Saxony, it forms subordinate masses in the Red Gneiss, and 
not far from Dippoldiswalde, in Saxony, it penetrates the grey 
gneiss of the Weissritzthal in distinct veins. 

References. 

Voltz, Geognosie de 1' Alsace, p. 55. 
Naumann, Erliiuter. zur geogn. Karte v. Sachsen. 1838, No. 2. 

p. 96. 

Cottain v. L. u. Br. Jahrb. 1853, p. 561. 
Delesse in the Ann. des Mines, [5] vol. x. p. 317, and Compt. 

rend. 1857, vol. xliv. p. 766. Ausz. in v. L. u. Br. Jahrb. 1858, 

p. 848, and 1860, p. 724. 
G. Leonhard, on Minette in the Odenwald Verhandl. d. nat. 

med. Vereins zu Heidelberg, vol. ii. p. 7, and v. L. u. Br. 

Jahrb. 1861, p. 495. 

H. Mutter Neues Jahrb. f. Min. 1865, p. 1. 
H. Pauly, Neues Jahrb. f. Min. 1863, pp. 257, 418. 
Th. Elray, Minette im Morran. Neues Jahrb. f. Min. 1863, 

p. 478, 1865, p. 745. 

(B) FRAIDEONITE. 

FRAIDRONIT. (Germ.) 
FRAIDRO^ITE, E. Dumas. (Fr.) 



MICA-TRAP ROCKS. 175 

A greenish fehitic principal mass combined with a greater or less 
quantity of mica. Iron pyrites and quartz occur as accessories. 

This composition so evidently resembles that of minette that 
it might well be considered as only a variety of that rock. 
Lan, however, adheres to the name of fraidronite, which had 
been already given by Dumas, and from the analyses which he 
made, pronounces it to contain a considerable admixture of 
chlorite, which he considered as the cause of its greenish colour. 
He also found carbonate of iron and lime, which he considered 
as accessory. Delicate veins of calcspar often pervade the 
whole mass of the rock. On weathering it crumbles into balls 
or a kind of grit. In the department of Lozere and in the 
Cevennes it forms dykes and veins in talc-schist, mica-schist, 
gneiss, and granite. Lan in the Ann. des Mines, [5J vol. vi. 
p. 412 ; v. L. u. Br. Jahrb. 1858, p. 609. 

(C) KERSANTON. 

KI;K> \vrnx. (Germ.) 

KlillSANTON. (Fr.) 

In a grwnuk-grty fekpathic matrix are contained hexagonal 
tabular crystals of mica, broion to black. Less frequently the 
matrix is granular, and contains crystals of felspar. 
Contains silica about 53 p. c. 

In the matrix, felspar usually predominates, which is not 
orthoclase, but most likely oligoclase. The distinct crystals 
of felspar are generally oligoclase. The mica is magnesian 
mica, which is not only an ingredient in the matrix, but some- 
times forms a coating round small globular grains (amygda- 
loids) of calcspar or quartz. Marcasite and magnetic iron-ore 
occur as accessories. Delicate veins of calcspar often run 
through the whole rock. 

The name of kersanton was first given by Riviere. The 
rock is evidently closely allied to the inica-porphyiite, minette, 
and kersantite. 

It abounds in the district of Brest, and Quimper in Brittany, 
where it is applied to building purposes. 

References. 

Riviere, intheBullet.de laSoc. gSol. deFr.,1844, [2] vol. i. p. 528. 
Dufrenoi, Expl. de la Carte ge"ol. de la France, 1844, vol. i. p. 198. 
Delesse, Ann. des Mines, 1851, vol. xix. p. 175, 

(D) KERSANTITE. 

KERSANTIT. (Germ.) 

\\ KKSANTITE (OlJGOCLASITE). ( Fr.) 

A fibrous or porphyritic compound of oliyoclase and mica, fre- 
quently containing some hornblende and quartz. 

Contains silica, about 64 p. c. 

Oligoclase generally predominates in the compact or fine- 
grained matrix of the rock, which sometimes is entirely com- 



176 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 

posed of that species of felspar, sometimes of oligoclase and mica. 
In this mass are enclosed crystals of oligoclase with brown 
stripings, and of white or greenish colour, or tinged with red 
by decomposition ; dark laminae of magnesia-mica, some small 
grains of quartz, and frequently some fibrous hornblende, espe- 
cially in the narrower veins formed by this rock, and, dispersed 
through the whole rock, very minute particles of magnetic 
iron -ore. 

Carriere also found some red garnet combined with horn- 
blende in places where the latter was more prevalent and the 
rock somewhat fissile. At Viesembach, in the Vosges Moun- 
tains, where the rock is broken through by metalliferous veins, 
it contains magnetic iron pyrites and common pyrites. It is 
amygdaloidal. In some places the amygclaloidal cavities are 
filled with quartz, chlorite, epidote, and calcspar. 

The porphyritic varieties of this rock (which owes its name 
to Delesse) are evidently closely allied to the porphyrites, or 
perhaps also to granite-porphyry; in other respects it very 
nearly corresponds with kersanton, from which it is, perhaps, 
only to be distinguished by its containing hornblende, and also 
more quartz than that rock, and by its texture being sometimes 
fissile. 

Near Viesembach and Sainte Marie, in the Vosges, this rock 
forms subordinate masses and veins in gneiss. The veins are 
often quite compact at their borders. Fournet observed a 
similar rock in the granite near Francheville in Brittany. 

Reference. 
Delesse, in the Ann. des Mines, 1851, vol. xix. p. 165. 



SYENITE GROUP. 

It has been a frequent practice to include under the 
name of syenite all granites containing hornblende. But 
as the genuine syenites contain little or no quartz, we 
consider it more accurate to exclude the first-named rocks 
from the syenite group, and range them under the head 
of granites (syenite-granites), confining the term syenite 
to those rocks which consist essentially of orthoclase or 
microcline and hornblende, such as the rock of the 
Plauenschen-Grund, near Dresden. Nevertheless there 
is no precise boundary to be drawn between these and 
the syenite-granites. As accessories, some mica and even 
quartz may occur in syenite, but they are not essential 
ingredients. This narrowing of the meaning of the 
term syenite appears to us the more justifiable, as these 
genuine quartzless rocks only contain 50-60 per cent, of 
silica, and therefore can be included in the basic group ; 



SYEXITE GROUP. 177 

whereas those containing quartz have 60 70 per cent, of 
silica, and so belong to the acidic group. It so happens 
that the derivation of the name presents no obstacle to 
our definition, since it is well known to have originated 
in the erroneous belief that the antique stones which first 
received the name of syenite came from Syene in Egypt, 
which was not the case. Roziere therefore proposed to 
alter the name to Sinaite, from Mount Sinai, where 
genuine syenite is found, whereas at Syene only granite 
occurs. Werner, who first introduced the name into 
scientific petrography, applied it to the quartzless rocks 
of the Plauenschen-Grund ; although afterwards, in his 
' Klassification der Gebirgsarten ' (1787), he called the 
same rock a greenstone. 

In the syenite group we also include miascite, zircon- 
syenite, and foyaite, as being closely allied to the genuine 
syenite. 

11. SYENITE. 

SYEXIT, Werner. (Germ.) 
SYENITE. (Fr.) 

A crystalline granular compound of orihoclase or micro- 
dine and hornblende, and usually some titanite. 

Spec, grav 27 2-9. 

Content of silica in the rock of the Plauenschen-Grund, 
near Dresden, 55 60. 

The orthoclase or microcline is usually the principal 
ingredient, and being in general red, it gives that colour 
to the whole rock, deepened into a brownish-red by the 
hornblende. There are, however, syenites whose orthoclase 
is nearly white, and others containing an admixture of 
oligoclase. The andesine, which Delesse considered he 
had found in some syenites of the Vosges^ is held by 
Rose to be a decomposed oligoclase. An indistinct fissile 
texture is sometimes occasioned by the parallel disposition 
of the felspar crystals (sometimes twins), and a porphyritic 
texture by the prominence of separate and larger twin 
crystals. The hornblende is occasionally developed in 
separate columnar crystals, but it usually only forms part 
of the general crystalline granular mass of the rock. Be- 
sides these, its two principal ingredients, syenite usually 
contains some titanite (or wohlerite), forming minute 

N 



178 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 

brown crystals of adamantine lustre, dispersed through 
the general mass, often only to be recognised with the 
lens. Some mica, quartz, elaeolite (nepheline), zircon, 
magnetic iron-ore, and pyrites, are also to be found in 
the general mass, but only as accessories and in small 
quantity. Epidote, which also occurs partly in the ge- 
neral mass, and partly in the crevices of the rock, is 
probably the product of a decomposition of hornblende ; 
and an invisibly small proportion of carbonate of lime, 
causing a slight effervescence with acids, is traced by 
Bischoff to the same origin. 

A larger proportion of mica and quartz occasions transi- 
tions into syenite-granite or syenite-gneiss ; an increase of 
elasolite and zircon, transitions into miascite and zircon- 
syenite. Again, many syenites contain oligoclase as well 
as orthoclase or microcline, opening up a transition into 
diorite, which latter is essentially nothing but a syenite 
containing oligoclase instead of orthoclase. This trifling 
difference, which is usually connected with a coarser tex- 
ture of the rock, may possibly only be a consequence of 
the different level at which it attained the solid state. We 
find, indeed, syenite in its bedding to be more decidedly 
plutonic than diorite. 

Varieties in Texture. 

(a) COMMON SYENITE. \ Uniformly granular, as in the Plau- 

( $KH enschen-Grund, near Dresden. 
(6) POBPHYRITIC SYENITE. \ With separate and larger crys- 

PORPHYRARTIGER SYENIT. (Germ.) > f -i f nr fi inP i Qca 
SYENITE PORPHYROIDE. (Fr.) J tals Ol rtnodase. 
Frh. von Richthofen has given the name of syenite-porphyry 
to a rock of this class found hi the Visena Valley, near Predazzo, 
in Tyrol. He desciibes it as consisting of a granular matrix of 
orthoclase, with little hornblende, and sometimes oligoclase in 
small quantity. The matrix enclosing twin crystals (three 
inches long) of orthoclase. 

It would be too much to say that there are no compact, 
vesicular, or amygdaloidal varieties of syenite ; we are 
only unable directly to trace any rocks of such textures 
through transition states from genuine syenite so as to 
show a direct connection with it ; and therefore we con- 
fine the name to the distinctly granular compound of 
felspar and hornblende, as above described. But amongst 
the aphanites there are certainly compact and vesicular 



SYEXITE GROUP. 179 

rocks, whose chemical composition, at least, is so exactly 
that of syenite, that under a slower and more plutonic 
process of cooling, they might well have become syenite. 
They bear the same relation to it as petrosilex to granite. 
That these compact rocks do not occur in geological con- 
nection with syenite may be owing to the thoroughly 
plutonic origin of the latter, causing it always and every- 
where to have cooled uniformly and very slowly. The 
same observation applies to granite. 

Properly speaking, there are no varieties of composition 
to adduce, unless we consider as such those transitions 
into granite and diorite which are occasioned by the 
occurrence of mica, quartz, and oligoclase. The zircon- 
syenite is rather a variety of miascite than of syenite 
proper. But this seems a fitting place in which to in- 
troduce the rock which Delesse has termed 

MiCA-DioRiTE. ] It consists of a crystalline granular 

(,!.!MMi.i;!)[oitrr. (Germ.)\ compound of hornblende, orthoclase, 
Ditmrr^MiCACi, Beta*, t oligocla5e) mica> md very little ^^ 

' generally of a dark colour, almost 

black. Content of silica only 48. From this composition we 
may regard this rock as something between diorite, syenite, 
and granite. In the Vosges it occurs in dykes in granite. 

Syenite is usually jointed into large irregular or thick 
tabular masses ; it forms entire mountains and occupies 
extensive regions ; only seldom forms distinct veins or 
dykes in other rocks, but is not unfrequently traversed 
by granitic veins, or it often contains granitic concre- 
tions. It is often associated v with great tracts of granite, 
and then passes over into syenite-granite, and finally into 
granite. The syenite of the Plauenschen-Grund, near 
Dresden, is eminently characteristic. Near Ditro, in Tran- 
sylvania, instead of titanite it contains much wohlerite. 

References. 

Xinimtmn on the Saxon Syenite, Erlauterung zur geog. Karte 

von Sachsen, 1845, No. 6, p. 116. 
L. van Such on the Monzon-syenite in v. Leonhard's Taschen- 

buch, 1824, p. 345. 
von Richthofen on Monzon-syenite, in Geogn. Beschr. v. Siid- 

Tyrol, 1860, p. 144, which contains, besides orthoclase and 

hornblende, some oligoclase, mica, and pyrites; ibid. p. 150. 
Zirkflj Syenit des Plauenschen-Grundes. * Poggendorf s Ann. 

vol. cxxii. p. 621. 

N 2 



180 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 

Delesse on Mica-diorite, in which he also includes rocks from 
the Kuhlenberg, near Harzburg, (gabbro ?) and from the 
Felsberg, near Darmstadt, in the Ann. des Mines, 1851, [4] 
vol. xix. p. 150. Karsten's Archiv. 1851, vol. xxiv. p. 280. 
Bullet, de la Soc. geol. de Fr. 1850, vol. vii. p. 524. The 
syenite rose cFEgypte here described is granite, Ann. des 




jnsyenit in v. L. u. Br. Jahrb. 1848, p. 
The following works on Syenite relate partly to rocks rich in 

quartz, which we class under the head of syenite-granite, 

viz. : 

v. Dechen in v. L. u. Br. Jahrbuch, 1858, p. 339. 
v. Rath in v. L. u. Br. Jahrbuch, 1858, p. 339. 
Streng in Poggend. Ann. 1853, vol. xc. p. 132. 
Kjerulfj Christiania Silurbecken, 1855, pp. 8, 12, and 15. 

12. MIASCITE. 

MIASCIT. (Germ.) 
MIASCITE. (Fr.) 

A crystalline compound of orthoclase, nepheline, socialite, 
and black mica ; coarse-grained to fine-grained (in 
the different varieties other minerals also occur). 

This rock was first discovered by G. Rose in the Ural 
Mountains. Its orthoclase is Breithaupt's Mikrokline, 
and is white or grey ; the nepheline is yellowish-white 
(elaeolite) ; lustre only slightly resinous ; the sodalite is 
grey or a fine blue ; the black mica is nearly unaxial. 
Besides these principal ingredients, the following occur, 
but frequently" only as accessories : davyne, wohlerite, 
zircon, magnetic iron-ore, pyrites, pyrochlore, cancrinite, 
apatite, monazite, even quartz, hornblende, &c. By means 
of these minerals, transitions take place into granite, 
syenite, and especially zircon-syenite. At Miask the 
texture of this rock is sometimes fissile ; at Ditro, in 
Transylvania, where miascite occurs at the margin be- 
tween syenite and mica-schist, and intimately blended 
with the former, the blue sodalite is frequently arranged 
in layers, and the texture is generally very unequal, 
sometimes quite coarse, sometimes fine-grained. 

References. 

G. Rose, Eeise nach dem Ural, vol. ii. pp. 47, 93, and 535, 
and Poggend. Ann. vol. xbii. p. 375. 



SYENITE GROUP. 181 

firrithaupt, Berg- u. Huttenin. Zeit. 1861, p. 493. 
t'otta, ibid. 1862, p. 73. 

Varieties in Composition. 

A. ZIRCON-SYENITE. 

ZJRKONSYENIT, Von Buch. (Germ.) 
SYENITE ZIRCONIENNE. (-fV.) 

A crystalline-granular compound of orthoclase, nepheline (elaolite), 
zircon, and usually only little hornblende. 

This rock is closely allied to miascite, both in respect of its 
essential and accessory ingredients. However, its composition 
varies so much in different places, that it is frequently difficult 
to decide what are essential and what accessory ingredients. 
The principal place where it occurs is the district of Laurvir 
and Brevig, in Norway: here there also occur eukolite and 
eudialite as accessory ingredients. 

References. 

L. v. Buch, Reise nach Norwegen, vol. i. p. 133. 
Ifamsmann, Reise nach Skandinavien, vol. ii. p. 103, and 
vol. x. p. 235. 

B. FOYAITE. 

FOYAIT. (Germ.) 

A crystalline granular compound of orthoclase-mepheline (elaolite), 
and hornblende. 

Spec. grav. . ** 2*6. 

The orthoclase is white or greyish-white, forms long tabular 
crystals with twin growth^(but not very perfectly developed), 
and is decidedly predominant. The reddish elaeolite of greasy 
lustre occurs in single hexagonal crystals. 

The greenish-black hornblende forms columnar crystals or 
small grains and parts of grains. The varieties of texture are 
the coarse-grained, fine-grained, compact, and porphyritic ; the 
latter contain crystals of orthoclase and elaeolite in a fine- 
grained matrix. The orthoclase crystals themselves some- 
times contain elaeolite and hornblende. The texture often 
changes very rapidly, as in gabbro. As accessories there 
occur titanite and magnetic iron-ore (very frequent), hexagonal 
brown laminae of mica, and iron-pyrites. 

This rock forms the mountains Foya and Picota in the pro- 
vince of Algarve in Portugal, where it is jointed in irregular 
masses. Blum has named it after the first mountain. 

Blum in von Leonhard's Jahrbuch, 1861, p. 426. 



182 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. 



ACIDIC IGNEOUS EOCKS. 

These rocks are compounds of orthoclase, sanidine, or 
oligoclase, with quartz, mica, or hornblende. 

They also contain many other minerals as accessories. 

Their proportion of silica is almost always above 60 
per cent., and extends in some cases to upwards of 80 
per cent. 

Their texture is generally granular or porphyritic, but 
sometimes compact or vitreous, seldom vesicular, and never 
amygdaloidal. Frequently they have a somewhat fissile 
or foliated structure, and so they even form transitions 
into certain of the crystalline schists. 

Like the basic rocks, they are divisible into the volcanic 
and the plutonic. 

1. Volcanic. 

In the rocks of this division the prevailing species of 
felspar is sanidine or oligoclase ; the labradorite (rich in 
lime), so often found with pyroxene in the basic rocks, 
is very rare in the acidic. The felspar is combined with 
some hornblende, and more rarely also with quartz, yet 
the rock always contains a large proportion of silica ; 
augite is only an accessory ingredient. 

The volcanic acidic rocks fall into two principal groups ; 
the trachytes and phonolites. The trachytic group, how- 
ever, contains many varieties both of composition and 
texture, and hence a great number of separate names, 
such as pearlstone, obsidian, &c. The trachytes occur 
as lava at active volcanoes of the present day, which is 
rarely, if ever, the case with the phonolites. Perhaps 
the latter are, to a certain extent, products of transmu- 
tation from compact or porphyritic trachytes. 

Although the trachytes, when characteristically deve- 
loped, differ very widely from the basalt, so that these 
two may be called the extreme products of volcanic 
agency, yet there are many volcanic rocks of intermediate 
character, which, to a certain extent, form transitions 
between the two groups, and prevent any very definite 



TRACHYTE GROUP. 183 

line of distinction between them. In many individual 
cases it is, in fact, difficult to distinguish trachytic from 
basaltic rocks. 

THE TRACHYTE GROUP. 

The term trachyte, signifying rough stone, was first 
introduced by Hatiy, to denote a crystalline granular com- 
pound, in which sanidine, as the predominant ingredient, 
is combined with some other felspar, with hornblende (or 
augite), mica, or even quartz, in subordinate quantities. 
The principal mass is sometimes fine-grained, or even 
compact, with distinct minerals porphyritically prominent. 

Soon after Haiiy had first called attention to this rock, 
many other rocks came to be observed, having the same 
mineral composition, differing somewhat from it in tex- 
ture, but connected with the normal trachyte by inter- 
mediate transition states. These were called trachytic 
rocks, without being reckoned as actual trachytes ; thus, 
for instance, trachyte-porphyry, pearlstone, obsidian, 
pumice-stone, and many compact as well as porous tra- 
chyte-lavas. 

Then it was discovered tfyat many of the rocks which, 
without accurate mineralogical investigation, had been 
taken for trachyte of the 'prescribed composition, con- 
tained an oligoclase-felspar instead of the sanidine for- 
merly considered so essential an ingredient ; but in other 
respects their trachytic character was preserved. Ac- 
cordingly, the trachytes came to be divided into sanidine- 
trachyte and oligoclase-trachyte ; these two varieties are, 
however, connected with each other by many transition 
states, and their geological position and character are 
identical. In compact or fine-grained states the difference 
between them is scarcely to be recognised ; the varieties 
of texture appear likewise to be essentially the same in 
both. 

It may be useful, before going on to the description of 
the individual trachytic rocks, to take a general survey of 
what have been described under that name, and the mode 
in which different writers have dealt with the different 
varieties. 

Before the difference as to the species of felspar was re- 
cognised or known, the following varieties of the rock were 



184 ACIDIC IGNEOUS KOCKS. (1) VOLCANIC. 

distinguished by Beudant (in his Voyage en Hongrie), 
and by Bur at (in his Description des Terrains vole, de la 
France centr. 1833), and also by Naumann. 

(a) TRACHYTES. 

Trachyte granitoide (granitic trachyte), e. g. at Handerlo, near 
Schemnitz. 

Fibrous or gneiss-like Trachyte, e. g. on the Pontellaria. 

Trachyte schistoide (schistous trachyte), e. g. at the Pas de 
Compain, department of Cantal in France. 

Trachyte a gros crystaux, a trachyte rich in felspar, at Dra- 
chenfels, near Bonn. 

Trachyte amphibolique, a trachyte rich in hornblende, e. g. 
near Schemnitz (perhaps the same as Breithaupt's timazite). 

Trachyte micace (micaceous trachyte), Monte Catini, in 
Tuscany. 

Domite, or Trachyte terreux (domite or clay stone-like tra- 
chyte), e. g. at the Puy de Dome. 

Trachyte porphyrolde (porphyritic trachyte), Schemnitz and 
Kremnitz in Hungary. 

Trachyte homogene (simple trachyte), frequently resembling 
phonolite, Monts Dores in Velay. 

Trachyte semi-vitreux (semi-vitreous trachyte), Tokay in 
Hungary; Iceland. 

Masenga, according to Naumann, the genuine trachyte of 
the Euganean Hills in Lombardy. 

Nenfro of Brocchi, according to Naumann, genuine trachytes 
of the Cimini Mountains. 

Nekrolite of Brocchi, according to Naumann, trachyte from 
Viterbo and Tolfa. 
(6) TRACHYTE-PORPHYRIES CONTAINING QUARTZ. 

Perlite-like Trachyte-porphyry. Hungary. 

Porous Trachyte-porphynj . Hungary. 

Vesicular Trachyte-porphyry (with globular cavities). Hun- 
gary. 

Millstone porphyry, or cavernous trachyte-porphyry. Miih- 
lensteinporphyr, or cavernoser Trachytporphyr. Porphyre 
meulier. Hliniker valley, in Hungary. 

Clay stone-like Trachyte-porphyry. Thonsteinahnlicher Tra- 
chytporphyr, Ponza Islands. 

(<?) Q.UARTZLESS TRACHYTE-PORPHYRIES. A 

Perlite-like Trachyte-porphyry, withom quartz. Hungary. 

Clay stone-like Trachyte-porphyry, wi^)iit quartz. Hungar} r . 

Pumice-stone-like Trachyte-porphyry, without quartz. Hun- 
gary. 

Slaty Trachyte-porphyry, without quartz. Ponza Islands. 
(d) PERLITES AND PEARLSTONE-PORPHYRIES. 

Perlite testace (granular shelly perlite). Telkebanya in 
Hungary. 

Spherolitic pcrlite or spherolite rock. Schemnitz in Hungary. 

Perlite retinitiqi{e (pitchstone-like perlite) ; Ofen in Hungary. 
Lipari Islands. 



TRACHYTE GROUP. 185 

Perlite porphi/rique (perlite porphyry), Hungary. 

Perlite litho'ide. compacte (clay stone-like perlite), Hungary. 

Perlite ponceaux (perlite pumice-stone), Hungary. 
(e) PURE OBSIDIAN. 

Porphyritic Obsidian, or obsidian-porphyry, spherulitic obsi- 
dian. 
(/) PUMICE-STONE. 

Obsidian pumice-stone. 

Perlite pumice-stone. 

Trachyte pumice-stone, 
(g) ANDESITE. 
(h) TRACHYTE-DOLERITE. 

In the decomposed states of trachyte, and especially in the 
so-called alumstone, we can of course not recognise the fresh 
state of the rock. 

The first thing which strikes us with reference to the 
foregoing catalogue is the great number and variety of 
rocks which may be included under the head of trachyte 
in its more extended signification. All the distinctions 
which have been made are, however, not equally important. 

Some varieties occur only in one locality, and some 
scarcely belong to the trachytes at all. 

In investigating a particular district, we should, of 
course, notice the smallest modifications in the nature of 
the rocks which come under our observation ; but for the 
purposes of definition in a general treatise like the present 
it is impossible, and would be undesirable, to record every 
trifling variety of texture and composition. 

G. Rose, in the 4th vol. of the ' Kosmos,' has proposed 
to subdivide all trachytic rocks into the six following 
groups : 

1. A rock whose principal mass consists entirely of crystals of 

vitreous felspar, which are tabular and usually large. Little 
or no hornblende and mica are contained in its composition, 
and are quite non-essential as ingredients Campi Phelegrai, 
Ischia, La Tolfa, &c. Augite shows itself in small crystals in 
the Mont Dore", but very rarely. In the Campi Phelegrai, 
where there is hornblende there is no augite, also no leucite, but 
of this last mineral Hoffman discovered some specimens at the 
Lake of Averno, and G. Rose on the cliffs of the Monte Nuovo. 

2. A rock whose principal mass contains single vitreous felspar crys- 

tals and a great number of small snow-white oligoclase crystals. 
The latter are frequently regular, and grown into the vitreous 
felspar, and form a covering round it. Sometimes a small 
proportion of hornblende and mica, and in some varieties 
aujnte, are found in it. 
The trachytes of Drachenfels and the Perlenhardt in the 



186 ACIDIC IGNEOUS ROCKS. (!) VOLCAXIC. 

Siebengebirge, and many varieties in the Mont Dore and Cantal, 
belong to this subdivision. 

3. These are dioritic trachytes whose principal mass contains many 
small oligoclase crystals with black hornblende and brown 
magnesian mica. To this species belong the trachytes of 
^Egina, the Kozelniker valley near Schemnitz, Nagyag in 
Transylvania, and Montabaur in Nassau, Stenzelberg and 
Wolkenburg in the Siebengebirge, Puy de Chauniont, near 
Clermont, and Liorant in Cantal. The Kasbegk in the Cau- 
casus, the Mexican volcanoes of Toluca and Orizaba, also the 
domites of L. v. Buch, belong to this subdivision. In the white 
fine-grained matrix of the trachytes of the Puy de Dome are 
enclosed vitreous crystals which have always been considered 
to be felspar, by which term Rose implies orthoclase, but the 
cleavage surfaces of which always show striae, and are, there- 
fore, in fact, oligoclase. (The above-named examples from 
Hungary and Transylvania belong to Breithaupt's timazite.) 

4. The principal mass contains augite and oligoclase. The peak of 

Teneriffe, the Mexican volcanoes, Popocatepetl and Colima, the 
South American volcanoes, Tolima, Purace near Popayan, 
Pasto, and Cumbal Ruca Pichincha, Antisana, Cotopaxi, Chim- 
borazo, Tunguragua. In Tunguragua, associated with the 
augite crystals, there occur small independent crystals of uralite 
of blackish-green colour (diabase or dolerite ?). 

5. A combination of labradorite and augite, a doleritic trachyte, 

^Etna, Stromboli, &c. (Why should not these rocks be genuine 
dolerites ?) 

6. A rock whose matrix is usually grey, in which crystals of leucite 

and augite are enclosed, with some olivine (very little). Vesu- 
vius and Somma ; also the extinct volcanoes Vulture, Rocca 
Monfina ; the Albanian Mountains and Borghetto. (This is 
the same as our leucite rock.) 

It will be seen that Rose's idea of trachyte is much 
more extended than is at all usual : it embraces almost all 
the volcanic rocks. 

More recently Freiherr v. Richthofen has divided the 
trachyte formations of Transylvania and Hungary into 
two classes the rhyolitic and trachytic. The latter are 
almost exclusively rocks containing hornblende and oligo- 
clase as their essential constituents. Sanidine is not the 
predominant felspar except in certain rocks of the most 
recent and subordinate eruptions ; so that, speaking gene- 
rally, according to von Richthofen, by far the greater 
proportion of the whole group of trachytes (proper) 
consists of oligoclase, and not of sanidine rocks. The 
silica is never so abundant as to develope distinct crystals 
of quartz. 



TRACHYTE GROUP. 187 

Von Richthofen subdivides the trachytes again into 
' greenstone trachytes ' and ' grey trachytes.' The former 
(our timazite) often correspond exactly with the oldest 
diorites and dioritic porphyries. The latter, on the other 
hand, consist principally of oligoclase and hornblende, 
with the occasional addition of some augite. 

Under the term rhyolite, Richthofen embraces all the 
most acidic (richest in silica) amongst the recent igneous 
rocks. He especially instances in Hungary the trachyte- 
porphyries, perlites, &c. (Vide L. u. 13. Jahrb. 1859, 
p. 304, and 1861, p. 98 ; Jahrbuch d. geol. Reichsanst. 
1860, Sitzungsber. p. 92.) 

These two groups of trachytes proper and rhyolites 
certainly appear of general geological importance ; they 
bear the same relation to each other, within the acidic 
group, as the acidic rocks bear to the basic ; and although 
in Hungary they both belong to one and the same great 
tertiary eruptive period, the rhyolites always appear the 
more recent of the two. 

We find similar phenomena in the rocks of all eruptive 
periods, the plutonic as well as the volcanic. Where 
syenites and granites occur together, the granite (rich in 
silica) is usually the most recent ; in the same way we 
often find veins of granite intersecting the gabbro (poor 
in silica). In the Thuringian Forest the quartz-porphy- 
ries are in general of more recent origin than the mica- 
porphyrites (poor in silica), although they both belong 
to the same great period. In the Bohemian Mittelge- 
birge, whose conical mountains consist partly of basalt 
and partly of phonolite, both of which appear to have 
been formed during the tertiary period, the phonolite 
(somewhat the richer of the two in silica) is found 
throughout as the most recent; so that putting all these 
facts together, we are almost justified in holding it for a 
universal law, that wherever igneous rocks rich in silica 
occur together with basic igneous rocks of the same great 
period of eruption, the former are of somewhat later 
origin than the latter. Basalt, nevertheless, sometimes 
forms an exception to this rule, as in Hungary, where it 
penetrates the trachytes ; but it is questionable whether 
the basalt in these cases may not belong to a separate 
period more recent still than the trachytes. 



188 ACIDIC IGNEOUS EOCKS. (l) VOLCANIC. 

If we find it impossible to define a precise boundary 
between the acidic and basic volcanic rocks, any more 
than between the volcanic and plutonic groups themselves, 
there can hardly be matter for surprise ; we should, 011 
the contrary, be at a loss to explain any such sharp dis- 
tinction if it existed. We find rocks of character' so 
undecided, that we may with almost equal justice group 
them with the greenstones as the trachytes. Such, for 
instance, is timazite. With others it may appear doubtful 
whether we should attach them to basalt or trachyte. Such 
are trachydolerite and andesite. The latter was in the first 
instance, without much inquiry, grouped with the trachytes 
because of its geological position and its rough texture. 
Subsequently the prevailing felspar species was taken for 
albite, and L. von Buch called the rock andesite from the 
Andes, where it occurs in great extent, to distinguish it 
from ordinary trachyte ; and although it has lately been 
discovered that the felspar is not albite but oligoclase, 
that does not seem to us to furnish a sufficient reason for 
changing the name of the rock (as proposed in e Kosmos'), 
if we wish to preserve any individuality for it at all. It 
may, however, remain questionable how the rock should 
be grouped. If we find with the oligoclase, pyroxene 
and hornblende occurring as essential and important in- 
gredients ; if the rock contains no quartz, but occasionally 
dark magnesia-mica, olivine, and titanite (and always 
magnetic iron-ore), then it may certainly be that andesite, 
if a volcanic product, should be assigned to the basalts ; 
or if plutonic, to the greenstones. Whilst, on the other 
hand, its somewhat high proportion of silica (59 67 per 
cent.), as well as its sometimes vitreous state, is opposed 
to this grouping, and gives the rock a more trachytic 
character. It is for these reasons a rock of middle cha- 
racter, of which there are many such. Roth even distin- 
guishes a pyroxene-andesite and an amphibole-andesite. 
With the first he classes many volcanic rocks of Iceland 
and TenerifFe ; with the latter, the so-called trachytes of 
Wolkenburg, and of Stenzelberg in the Siebengebirge, the 
domite of the Puy de Dome, and many lavas of ./Etna. 

The trachytes often form an essential part of the pro- 
ducts of active volcanoes, and form actual lava streams. 

They are also frequently found at so-called extinct 



TRACHYTE GROUP. 189 

volcanoes; and form single conical hills or connected 
groups of mountains in districts where, since the tertiary 
period, no eruptions have taken place. These last-men- 
tioned older trachytes approach in character the plutonic 
rocks. We are, however, unacquainted with any trachytes 
which arc certainly older than the Tertiary period. 

AYe propose, with Von Richthofen, to divide all the 
trachytic rocks into two separate sub-groups (trachytes 
and rhyolites), the differences between which are more 
marked than those of the several varieties of mere texture 
and composition. These latter differences are, however, 
important enough to deserve a more special notice than 
the corresponding varieties of many other rocks ; and 
we shall, therefore, accord them a full description, merely 
premising in general that theyare apt to run one into the 
other by gradual transitions occasioned by the prepon- 
derance or the reverse of a principal ingredient. 

13. TRACHYTE. 

TRACHYT. (Germ.') 
TRACHYTE, Haiiy. (Fr.} 

A compound of sanidine, oligoclase (or even albite and 
labradorite), ivith some hornblende or augite and dark- 
coloured mica. A rough principal mass in which, as 
matrix, some of its mineral constituents are jrequently 
distinctly and separately developed and imbedded. 

Spec, grav 24 2-8 

Contains silica .... 50 67 p. c. 

As a rule, in all trachytes the felspar is predominant. 
The detailed grouping of their different mineral ingre- 
dients will appear from the description which we give 
below of the several varieties in composition. 

Varieties in Texture, 
(a) GRANULAR TRACHYTE. 

KMKMGER TRACHYT. (Germ.) 
TRACHYTE GRAxrrolDE. (Fr.) 

(5) PORPHYRITIC TRACHYTE. \ 

PORPHYRARTIGER TRACHYT. (Germ.) \ With larffe felspar Crystals. 
TRACHYTE PORPHYHOIDE. (Fr.) ) 

(c) COMPACT TRACHYTE. ) ( Or of * 8tat * Yei 7 nearl y 

/..KM..,, Hmn.TKK TRACHYT. (Germ.)\ approaching the compact.) 
TRACHYTE LITHOH>E. (Fr.) ) Also somewhat porphyritic. 



190 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. 

(d) VESICULAR TRACHYTE. ^ often, par excellence, called Tra- 

BLASIGER TRACHYT. (Germ.) r T , / 
TRACHYTE VACUOLAIRE. (Fr.) ) ch V te iam ' 

(e) DECOMPOSED TRACHYTE. \ Manv decomposed varieties are 

ZERSETZTER TRACHYT. {Germ.) called Alumstone, on account of 
TRACHYTE DECOMPOSE. (Fr.) ) their containing alum. 

Varieties in Composition. 

(A) SANIDINE-TRACHYTE. 

SANIDIN-TRACHYT. (Germ.) 

An aggregate of sanidine crystals, with some hornblende or mica as 
subordinate ingredients. Texture coarse or fine- grained to compact. 

Spec. grav. . ... . . . . 2 -4 2-6 

Contains silica - . : . . / . - r 59 60 p. c. 

In this compound, principally consisting of sanidine, horn- 
blende, and magnesia-mica, occur, as accessory ingredients, 
magnetic iron-ore, sodalite, olivine, titanite, and augite or 
quartz. It further appears probable, from the frequent pre- 
ponderance of the proportion of soda over the potash in the 
whole rock, that the compact matrix which permeates the 
whole nias?, cementing the distinct and recognisable minerals, 
contains, in addition to those we have mentioned, some mineral 
rich in soda, such as oligoclase, sodalite, or nepheline. The 
sanidine often occurs in a porphyritic form. The colour of the 
rock fluctuates between greyish-white and dark-brown grey. 
In most cases the texture is porphyritic, with granular or 
sometimes compact matrix ; some varieties are vesicular, and 
at the surface even scoriaceous, but not amygdaloidal. By 
decomposition a state is produced, not wackenitic, but more 
resembling claystone. The mass then appears almost white, 
whereas, in fresh condition, it is often very dark-coloured. 
The rock is generally of irregularly jointed structure. 

To this species belong, according to Roth, the trachytes of 
Rabertshausen, in the Grand Duchy of Hessen ; of Kappellen- 
berg (which contains some pyrope) ; of Mondhalde and Silber- 
brunnen, at the Kaiserstuhl j of Gleichenberg, in Styria ; of 
Monte Olibano, near Pozzuoli. Likewise the lavas found at 
Monte Nuovo, and those of the Azores, &c. 

The grey porous sanidine-trachyte, which occurs at the 
Laager lake, contains a good deal of haiiyne. 

(B) SANIDIXE-OLIGOCLASE-TRACHYTE (DRACHENFELS TRACHYTE). 

SANiDrsr-OLiGOKLASTRACHYT. (Germ.) 

A crystalline compound of sanidine and oligoclase with mag- 
nesia-mica and hornblende, also some augite, magnetic iron-ore, 
and titanite. 

Spec, grav 2'6 2-7 

Contains silica . . . . 60 67 p. c. 

This very characteristic rock of the Drachenfels, near Bonn, 
with its large sanidine crystals porphyritically enclosed in 
granular matrix, served a long time as the principal type of the 



TRACHYTE GROUP. 191 

trachytes, and all the felspar in that rock was assumed to be 
sanidine. Now, however, it appears, from the very consider- 
able quantity of soda contained in the matrix (up to 5 per 
cent.), that tlie latter probably consists principally of oligoclase. 
It is especially worthy of remark tnat in this porphyritic 
trachyte the large sanidine crystals frequently assume a parallel 
position to each other ; they are also sometimes broken in 
two, but both pieces still lie close together imbedded in the 
matrix. According to Roth, to this class belong the trachytes 
of Kiihlsbrunnen, in the Siebengebirge, and Freienhauschen, in 
the Eifel ; also, according to Richthofen, many trachytes of 
Hungary and Transylvania. 

(C) OLIGOCLASE-TRACHYTE (DOMITE). 

OLIGOKLAS-TRACHYT. (Germ.) 
DOMITE. (Fr. ) 

In this rock oliyoclase is the only recognisable felspar, as it con- 
tain* no xaniiliitc. The oligoclase is combined with some horn- 
blende or anyite and dark-coloured mica. 

These trachytes have been the least accurately analysed of 
any. They contain many other accessory minerals. *If the 
quantity of hornblende be above the average, then they pass 
into greenstones, e.g. into the greenstone-trachyte of Richt- 
hofen, or the timazite of Breithaupt. Whether andesite 
and trachydolerite should be included here may be doubtful. 
We prefer to treat them separately. This variety occurs in a 
tolerably fresh state at Stenzelberg', and at Wolkenburg, in the 
Siebengebirge. At the Puy de Dome, on the other hand, it is 
much decomposed, rough, almost crumbly, and is there called 
domite. It would be hazardous to attempt to distinguish 
varieties of texture. 

At Stenzelberg this rock exhibits a singular cylindrical 
jointed structure, in so-called 'outliers,' which consist of round 
columns, composed of concentric layers. Usually its structure 
is massive. 

(D) ANDESITE. 

ANDESIT. (Germ.) 
ANDESITE. (Fr.) 

A fine-grained or compact, and sometimes mtreous matrix, usually 
of dark-grey to black colour; contains crystals which, accord- 
ing to G. Rose, are oligoclase and augite. According to Abich, 
on the other hand, they are albite or oligoclase; and Abich 
adds, that some sanidine and hornblende, and always tiwyni'tic 
iron- ore, are likewise found in the rock. Dark-coloured mica 
frequently also occurs. 

Spec. grav. ,.;.. . . . 2-62-7 
Contains silica 50 67 p. c. 

Roth distinguishes an amphibole-andesite and a pyroxene- 
andesite, but as the latter likewise contains some hornblende, 
this distinction would be difficult to maintain. To the amphi- 
bok-endesites, according to him, the localities which we have 



192 ACIDIC IGNEOUS ROCKS. (1) VOLCANIC. 

above given under the head of * oligoclase- trachyte ' apply ; 
to the pyroxene-andesite, many volcanic rocks of Iceland and 
Tenerifte. 

This rock was first named by L. v. Buch, and its felspar was 
taken to be entirely albite. G. Kose could only discover oligo- 
clase in it. Doubts have also arisen respecting the other in- 
gredients. The matrix is sometimes easily to be reduced to 
powder. Known localities of its occurrence are : Pinchincha, 
Chimborazo, Antisana, and Cotopaxi j according to Abich, also 
the Caucasus and Mount Ararat. 

(E) TRACHYDOLERITE. 

TRACHYDOLERIT. (Germ.} 
TRACHY-DOLERITE. (Fr.^ 

A compound of oligoclase (or labradorite) with hornblende or 
augite, some magnetic iron-ore, and frequently also mica. These 
minerals lie imbedded in a grey or brown matrix. 

Spec, grav 2-72-8 

Contains silica . . . . . 54 61 p. c. 

We may here distinguish the varieties which contain horn- 
blende from those which contain augite j the latter are very 
nearly related to dolerite. 

Vesicular varieties also occur. Abich, who first distinguished 
this rock and gave it its name, designates the following places 
where it is found : The Peak of Teiieriffe, the Schivelutsch in 
Kamtschatka, the island of Liscanera, near Stromboli, and the 
older lavas of ./Etna, for the varieties which contain hornblende ; 
and the top of the crater of Stromboli, and the central cone of 
the Rocca Monfina, for those containing augite. 

Deiters recognised in the rock of the Lowenburg, in the 
Siebengebirge, a complete transition grade between trachyte 
and dolerite. Under the microscope its principal mass appears 
to consist of crystalline felspar (either oligoclase or labradorite), 
imbedded in which lie scattered crystals of striated felspar, 
of hornblende, augite, magnetic iron-ore, and even some olivine. 
The content of silica here diminishes to 52 per cent. 

References. 

Beudant, Vovage en Hongrie, translated (into German) by 

Kleinschrod, 1825. 
Abich, Vulkanische Erscheinungen, 1841 j Vulkanische Bil- 

dungen, 1849; Natur des armenischen Hochlandes, 1843, 

p. 25 j and Poggendorf 's Annalen, 1840, vol. 1. p. 345. 
Bunsen, in Poggendorf 's Annalen, vol. Ixxxiii. p. 197. 
Sartorius v. Walterhausen, Die vulk. Gesteine in Sicilien und 

Island, 1853. 
Schill, in G. Leonhard's Beitr. z. mineral. Kenntn. von Baden, 

1854, No. 3, p. 46. 
Deville, Sur le Trachytisine d. Eoches, in Compt. rend. 1859, 

vol. xlviii. p. 16. 
Enyelbach, in the Erlauter. d. geogn. Karte von Hessen. Sect. 

Schotten. Darmst. 1859, p. 43. 



TRACHYTE GROUP. 193 

Rammehberg, in Zeitschr. d. d. geol. Ges. 1859, vol. xi. p. 434. 

Zirkel, Die trachytischen Gesteine der Eifel, in Zeitschr. d. d. 
geol. Ges. 1859, vol. xi. p. 507. 

L. v. Buch on Andesite, in Poggendorf 's Ann. vol. xxxvii. p. 189. 

v. Dechen gives eight divisions of trachyte in his Geogn. Beschr. 
des Siebengebirges (Verhandl. d. nat. Ver. d. Rheinlande, 
1852). He appears, however, to have abandoned these in 
his more recent ' Geogn. Fiihrer durch d. Siebengebirge.' 

Zehler observed, in 1837, as many as forty different trachyte 
varieties in his l Siebengebirge.' 

Vom Rath, in his treatise, ' Die Trachyte des Siebengebirges,' 
1860, makes the following divisions : 

1. Drachenfels trachyte, whose white or grey matrix con- 
tains crystals of vitreous felspar and oligoclase, and some 
magnesia-mica and hornblende; accessorily, titanite, mag- 
netic iron-ore, augite, and apatite. Content of silica, 65 66. 

2. Wolkenburg trachyte. 1 he colour of the matrix from grey 
to black, or sometimes reddish. It contains crystals of oligo- 
clase, no vitreous felspar, but some hornblende and magnesia- 
mica. Accessorily, augite, olivine, magnetic iron-ore, pyrites, 
and perhaps some quartz. Content of silica, 59 62 per cent. 

3. Trachyte of Rosenau (not in connected rocks, only found 
in blocks). The base contains crystals of vitreous felspar, 
no oligoclase, more rarely some magnesia-mica, hornblende, 
sphene, and magnetic iron-ore. Content of silica, 78*8. 

The matrix appears in all these three varieties to be prin- 
cipally felsitic. Acid produces a weak effervescence, which 
may well be owing to carbonates of later origin than the 
rock itself, and the small quantity of zeolite which occurs is 
in all probability the result of decomposition. 

Vom Rath, Ueber Trachyt d. Enganeen. Zeitschr. d. deutschen 
geol. Ges. 1864, pp. 254-498. 

Deitei-s, Die Trachytdolerite des Siebengebirges, in Zeitschr. 
d. d. geol. Ges. 1861, p. 99. 

v. Richthofen, in the Jahrbuch d. geol. Reichsanst. 1860, Sitz- 
unjrsber. p. 92; extract in von L. u. Br. Jahrbuch, 1859, 
p. 304, and 1861, p. 98 ; Jahrb. d. geol. Reichsanst. 1864, p. 7. 

Stache has given the name of DACIT to a quartzose trachyte of 
Transylvania. Geogn. Beschr. von Siebenbiirgen. 

14. KHYOLITE. 

RHYOLITH. (Germ.) 

A compact, enamel-like, or vitreous matrix enclosing 
grains or crystals of sanidine, oligoclase, mica, or 
even quartz. 

Spec. grav. . , , * 2'3 2-6 
Contains silica 67 82 p. c. 

The matrix, which should, strictly speaking, always be 
of a prevailing felsitic character, varies however from the 

o 



194 ACIDIC IGNEOUS KOCKS. (l) VOLCANIC. 

simple compact to the vitreous state. It is distinguished 
from that of the trachyte proper by its larger proportion 
of silica; and the same difference in the proportion of 
silica is found to obtain between the trachytes and rhyo- 
lites in the collective analysis of each rock in its entirety. 
Hence in rhyolite free quartz appears much more fre- 
quently than in genuine trachyte ; on the other hand, the 
former contains no hornblende or augite, or, at least, 
those minerals are much more rarely found in it than in 
trachyte. 

Under the common name of rhyolite we comprehend 
the following principal varieties : Trachyte-porphyry, 
perlite, obsidian, and pumice-stone, all of which possess 
sub-varieties. 

A. TKACHYTE-PORPHYKY. Liparite. 
TRACHYTPORPHYR, LITHOIDIT in part. (Germ.) 

PORPHYRE TRACHYTIQUE. (Fr.) 

A compact felsitic matrix containing crystals of felspar, 
and sometimes also mica or quartz. But as this 
general definition essentially agrees with that of 
many porphyrites and quartz-porphyries, it is per- 
haps better to say : Trachyte-porphyry is the name 
given to those rocks (prevalently felsitic and porphy- 
ritic with a compact matrix) which are geologically 
allied to the trachytes. 

Spec, grav 2-42-6 

Contains silica ...... 67 81 p. c. 

The trachyte-porphyries are, as a rule, much richer in 
silica than the trachytes proper which we have described 
above. Their matrix is of prevalent felsitic composition 
and character, scarcely to be distinguished from that 
of the quartz-porphyries, and it only very rarely and 
exceptionally contains some traces of hornblende. 

Some trachyte-porphyries even contain grains or crys- 
tals of quartz or mica, or of both those minerals together, 
and thereby their resemblance to quartz-porphyry, gra- 
nite-porphyry, or mica-porphyrite, becomes still greater, 
and in fact so great, that occasionally, in the form of 
single specimens, it is impossible to tell the difference. 
In these cases, the only real difference consists in their 
geological connection with genuine trachytes or their 



TRACHYTE GKOUP. 195 

petrographical transition into perlite or pumice-stone. 
The felspar of the distinctly developed crystals in 
trachyte-porphyry is most usually oligoclase, but some- 
times also sanidine ; both of these also occur in quartz- 
porphyries. 

The most important varieties in texture, but which 
may almost all be divided into those with, and those 
without, quartz, are t 

(a) COMMON TRACHYTE-PORPHYRY. ) Its felsitic matrix is compact 
GEMEIXER TRACHYTPORPHYR. (Germ.) > i n fresh fracture, and fre- 
quently somewhat shining ; usually light-coloured, containing 
(more "or less plentifully dispersed) crystals of sanidine or 
oligoclase, mica, or sometimes quartz. At the Schlossberg of 
N'-usohl the matrix is of greenish colour, compact, with crystals 
of felspar, mica, and quartz, ^n the Hliniker valley, near 
Schemnitz, the matrix is yellowish, and especially distinguished 
for its crystals of mica. 

(/>) PERLITE-LIKE TRACHYTE-PORPHYRY. ) The matrix is often 
PERUTAHNLICHER TRACHYTPORPHYR. (Germ.) f somewhat enamel- 
like, and contains, besides those crystals which we have men- 
tioned, small compact balls of felspar (spherulites), frequently 
with radial fibrous texture, sometimes also grains of quartz 
and mica. These rocks pass over by transition into perlite. 

(e) ARGILO-TRACHYTE-PORPHYRY. ) The matrix is dull 

THOXSTKIXAHXUCHER TRACHYTPORPHYR. (Germ.) J or earthy, and usu- 
ally penetrated with firm veins or nests of harder texture. 
Bereghasz in Hungary. 

(d) VESICULAR or CAVERNOUS TRACHYTE-] The matrix contains 
PORPHYRY, MILLSTONE PORPHYRY, (round vesicular cavi- 

BLASIGER oder CAVI:IL\OSKK TRACHYTPOR- f ties, or 18 entirely pene- 

PHYR, MUHLSTEINPORPHYR. (Germ.) J * 



regularly shaped cavities, whose sides are sometimes partly 
coated with cnalcedony or quartz. 

These cavities, however, are never entirely filled, so as to 
form genuine amygdaloids. Hliniker valley near Schemnitz. 
(e) PUMICEOUS TRACHYTE-PORPHYRY. ) Forms a transition 

BlMSTEDCAHNLICHER TRACHYTPORPHYR. (Germ.) J f rom the Vesicular 

variety into pumice-stone. 

( f) SLATY TRACHYTE-PORPHYRY. ) The slaty texture is pro- 

SCHIEFRIGER TRACHYTPORPHYR. (Germ.) j duced by the manifold 
alternation of their layers of somewhat differing composition. 

Forchhammer has designated certain varieties of trachyte-porphyry 
which occur in Iceland by the special names of Krablite and Baulite. 
According to Bunsen, these are compounds of orthoclase and quartz. 

All these varieties abound in certain trachyte regions, as, for in- 
stance, in the neighbourhood of Schemnitz in Hungary, in the 
Euganean Hills, on the Ponza Islands and the Lipari Islands. They 
are usually irregularly cleft into angular masses, with columnar or 
tabular jointed structure. 

o 2 



196 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. 



References. 

Beudant, Voyage en Hongrie, 1822, in many places. 
Poulet Scrope, Ponza Islands, in Transact, of the Geol. Soc. [2] 

vol. ii. p. 195. 
AUch, Vulkanische Bildungen, 1849, p. 23. Vulkanische Er- 

scheinungen, 1841, p. 20; Geol. N. d. armenischen Hoch- 

landes, 1843, p. 44. 

K. v. Hauer, Jahrbuch d. Geol. Keiclisanst. 1859, p. 466. 
Forchhammerj in the Journ. f. prakt. Chemie, 1843, p. 390. 
Bunseri, in Poggend. Annalen, 1851, vol. Ixxxiii. p. 201. 

B. PEKLITE. Pearlstone, Pearlstone-porphyry. 
PERLIT. (Germ.} 
PERLITE. (Fr.} 

An enamel-like matrix containing round grains, several 
of which are constructed with concentric layers. 

Spec. grav. . . . . .' . 2-32-4 

Contains silica . . " . . . - 70 77 p. c. 

The whole mass of the rock perlite is of the same com- 
position as that of trachyte-porphyry, except that, on an 
average, it is somewhat more rich in silica. The state, 
however, of this compound, which is distinguished as 
perlite, often alternates with the simple compact obsidian 
state, or that other state which has become porphyritic 
by the occurrence of sanidine crystals. It also forms 
transition states into pumice-stone. Occasionally there 
occur, in addition to the sanidine crystals, some small 
mica flakes, red garnets, and even crystals of quartz. 
According to texture, Beudant distinguishes the follow- 
ing varieties : 

(a) GRANULAR SHELLY PERLITE. 

KORNIGSCHALIGER PERLIT. {Germ.) 

TRACHYTE TESTACE. (Fr.) 

(b) SPIUSRULITIC PERLITE. ^ with compact or radial striped 

ICHER PERLIT. Germ. 



SPHAROLITISCHER PERLIT. (Germ.) 
PERLITE GLOBULAIRE. (Fr.) 

(c) PERLITE-PORPHYRY. 

PERLITPORPHYR. (Germ.) 
PERLITE PORPHYROIDE. (Fr.) 

(d) VITREOUS, WITH RESINOUS LUSTRE. 

PECHSTEINARTIGKR PERLIT. (Germ.) 

(e) ARGILLACEOUS PERLITE. 

THONSTEINARTIGER PERLIT. (Germ.) 

(/) PUMICEOUS PERLITE. 

PERLTTBIMSTEIN. (Germ.) 

All these varieties are found (for instance) in the trachytic regions 
of Hungary, near Schemnitz, Tokay, Telkebanya, &c., near Zimapan 
in Mexico, on the Lipari Islands, &c. 



TRACHYTE GROUP. 197 

References. 

Beudant, Voyage en Hongrie, vol. ii. p. 363. 
v. Pettko, in Haidinger's Abhandlungen, 1847, vol. i. p. 298 ; 

and as to Schemnitz, in the Abhandlung. d. geol. Reichstanst. 

1853, vol. ii. No. 1. He names the variety with felsite balls 

' Spherolite rock.' 

Erdmann, Journ. f. tech. Chemie, 1832, vol. xv. p. 38. 
Delesse. Bullet, de la Soc. ge*ol. 1864, [2] vol. xi. p. 109 ; v. L. 

u. Br. Jahrb. 1856, p. 195. 

C. OBSIDIAN and PUMICE-STONE. 

OBSIDIAN und BIMSTEIN. (Germ.} 
OBSIDEENNE et PONCE. (Fr.) 

Obsidian is a volcanic glass, sometimes porphyritic by 
reason of sanidine crystals : this glass, however, when 
it becomes vesicular, passes over into the most exquisite 
foam-like pumice-stone. 

Spec. grav. . ' . ' . . " . " . 2*3 2*5 
Contains silica . , . , . . . 7182 p. c. 

This glassy or frothy texture belongs only to the rocks 
of the trachyte group, and more especially to the tra- 
chyte-porphyries or rhyolites. Their colour is (in the 
case of obsidian) usually dark black, brown, or greenish ; 
in the case of pumice-stone, on the other hand, white or 
yellowish-grey. According to differences of texture, we 
may distinguish : 

(a) COMMON OBSIDIAN. ) 

GEMEINER OBSIDIAN. (Germ.) \ A mere glass. 

OBSIDIENNE COMMUNE uraotDE. (Fr.) ) 
(6) OBSIDIAN-PORPHYRY \ with sanidine crystals, or some- 

OBSIDIANPORPHYR. (Germ.) [ t: mpa n l sn mi nlatps 
OBSIDIENNE PORPHYROIDE. (Fr.) ) Umes al80 mica P lates - 
(c) SPH^RULITIC OBSIDIAN. \ With felsite balls, passing 

SPHAROLITISCHER OBSIDIAN. (Germ.) } nvpr intr nprlifp 
OBSIDIENNB GLOBULAIRE. (Fr.) j over " to P er lte ' . 

{This rock is often of 
such long fibre and so 
nnrniid that it will PVPTI 
porous tnat it will even 
float on water. 

These species of volcanic glass are only found in trachytic volcanic 
regions. They are very characteristically developed at the Peak of 
Tenerifle, the Lipari Islands, in Iceland, in Mexico, &c. 

References. 

Beudard, Voyage en Hongrie, vol. iii. p. 389. 
Erdmann, Journ. f. techn. Chem. 1832, vol. xv. p. 36. 
K. v. Hauer, Jahrb. d. g. Reichsanst. 1854, p. 808. 
Damour, Poggend. Ann. 1844, vol. Ixii. p. 287. 



198 ACIDIC IGNEOUS EOCKS. (l) VOLCANIC. 

Mundoch, Phil. Mag. and Journ. 1844, [2] vol. xxv. p. 495. 
v. d. Boon-Meesch, Pogg. Ann. 1828, vol. xii. p. 616. 
Herter, Perlstein. Zeitschr. d. deutschen geol. Gesellsch. vol. xv. 
p. 459. 

PHONOLITE GKOUP. 

15. PHONOLITE, CLINKSTONE. 

PHONOLITH, KLINGSTEIN, PORPHYKSCHIEFER. (Germ.) 
PHONOLITHE. (Fr.} 

A compact base or matrix, in its, fresh state dark 
greenish-grey, showing here and there single cleavage 
surfaces of a vitreous felspar. The mass is as a rule 
somewhat slaty or schistose in texture, or of thinly 
tabular jointed structure gives a clear sound when 
struck by the hammer ; on weathering a sharply 
defined white crust is formed. 
Spec. grav. . . ..'.". 2-4 2'6 

Contains silica . . , , , / 50 62 p. c. 

Klaproth proposed the name of phonolite for this rock, 
as having a more scientific air than that of klingstein, 
previously in use, of which it is the translation, and 
the new name has been very generally accepted. The 
peculiar properties of the rock had long been recognised, 
its difference from basalt, trachyte, felsite rock, &c., but its 
exact ingredients had not been investigated. Gmelin first 
drew attention to its analysis by muriatic acid, in which it 
is partly soluble and partly insoluble. The soluble part was 
considered to be a zeolitic substance, the latter a felspar, 
and the whole was considered to be an intimately blended 
compound of zeolite and felspar (sanidine). 

By the more exact microscopic and chemical investi- 
gations of later times, however, it has appeared that the 
composition of the phonolite mass is not so simple, and is 
in some part wholly different from what was supposed. 
It is even questionable whether in its fresh state it con- 
tains any zeolitic substance at all ; certain is it that the 
nepheline crystals which both Breithaupt and Rose early 
recognised in phonolite, as well as the mineral forming 
part of the matrix which Rammelsberg also judged to be 
nepheline, have frequently been mistaken for zeolite. 

Gr. Jenzsch ventures to give the following as the mine- 
ralogical composition of this rock, after investigating mi- 
croscopically and chemically several very characteristic 
phonolites of Bohemia : 



PHOXOLITE GROUP. 199 

Per cent. 

Sanidine, estimated at 63-55 

Nepheline, do 31-76 

Hornblende (arvendsonite) . . . . 9-34 

Titanite ,. > 3-67 

Pyrites , . .* . . . 0'04 

These proportional values must, of course, vary greatly 
with locality. 

As accessories, the following minerals occur, and are 
sometimes distinctly to be recognised in the rock ; viz. 
oligoclase, augite, magnetic iron-ore, olivine, hatiyne, 
brown mica, leucite, and nosean ; the last two minerals 
are the least frequent. It is possible that the zeolite 
(natrolite) which sometimes fill^ the crevices of the rock 
may also occur in the principal mass, but if so, it is 
probably the result of decomposition. 

In respect of the proportion of silica contained in pho- 
nolite, we might equally well group it with the basic as 
the acidic igneous rocks ; it forms one of the intermediate 
links between the two. As it never contains quartz dis- 
tinctly and separately developed, it might seem to be 
more allied mineralogically to the basic rocks ; but geo- 
logically its character is nearer that of the trachytes 
than the basalts. Where it occurs together with the 
latter, as is very frequently the case, it seems to play the 
same part as the trachytes under similar circumstances. 

Its small content of water (0-6 0*8 per cent.) appears 
to be (at least in part) a secondary product, the result of a 
commencing decomposition ; and in the same manner the 
occurrence of many accessory minerals in the mass, more 
especially those appearing in the clefts and vesicular 
cavities. 

Phonolite often acquires a porphyritic texture from the 
prominence of distinct crystals of sanidine and acicular 
hornblende. The most marked porphyritic varieties are 
as a rule little slaty and somewhat decomposed. As de- 
composition progresses, the crystals become more promi- 
nent, and even the titanite then is frequently to be easily 
recognised. Many phonolites are dark-spotted, or they 
contain round grains of peculiar composition and colour ; 
these, however, as in the case of basalt, appear chiefly to 
arise from commencing decomposition. Many are en- 
tirely decomposed (kaolinised), and show an earthy frac- 



200 ACIDIC IGNEOUS KOCKS. (l) VOLCANIC. 

ture, with a light colour. Whole mountains of phonolite 
have, apparently at least, decayed in this manner, with 
scarcely a trace of slaty texture remaining. Naumann calls 
this variety Tr achy tic phonolite \ it is almost the only variety 
in which vesicular and amygdaloidal texture is found ; it 
never occurs in the fresh, dark, and slaty kinds. Jenzsch 
is even of opinion that the apparent vesicular and amyg- 
daloidal cavities of the phonolite are not genuine bubbles 
of the original rock, but have arisen subsequently by a 
kind of corrosive process of decay. This view certainly 
agrees with the absence of cavities in the perfectly fresh 
rock. Yet in some few phonolites are found very decided 
vesicular cavities. These cavities, as also the clefts and 
fissures, most usually contain zeolites ; especially apo- 
phyllite, chabasite, comptonite, desmine, natrolite, anal- 
cime, or calcspar and hyalite. 

Varieties in Texture. 

(a) COMMON PHONOLITE. ^ Dark-coloured, compact, schistose, 

GEMEINER PHONOLITH. (tar.) > O r imperfect slaty cleavage, and 
PHONO COMMUNE. (Fr.) ) ^ * 



the hammer. Mileschauer in Bohemia; Milzburg on the Ehon 
Mountain. 

(6) PORPHYRITIC PHONOLITE. ) The same mass with dis- 

PORPHYRARTIGER PHONOLITH. (Germ.) [ tinct crystals of hornblende, 
PHONOLITHE PORPHYROIBE. (Fr.) J au ^ te / or sanidine . Aussi ^ 

and Jakuben, near Tetschen in Bohemia. 

(c) TKACHYTIC PHONOLITE. ) Not slaty, not clinking, 

TRACHYTAHNLICHER PHONOLITH. (Germ.) j rough, of a rather light- 
grey colour ; frequently porphyritic, geodic, or amygdaloidal. Aussig, 
in JBohemia. 

(d) SPOTTED PHONOLITE. ] Luschwitz. near Aussig. in Bo- 

GEPLECKTER PHONOLITH. (Germ.) Y i^ arn : Q 
PHONOLTTHE TACHETEE. (Fr.) ) L lld< 

(e) VESICULAR PHONOLITE. j Blattendorf, nearHaida, in Bo- 

BLASIGER PHONOLITH. (Germ.) \ V.Q:,, 
PHONOUTHE VACUOLAIRE. (Fr.) ) " 

(/) AMYGDALOIDAL PHONOLITE. ^ Marienberg, near Aus- 

MANDELSTEINARTIGER PHONOLITH. (Germ.) [ -R^p,.,:,, 
PHONOLITHE AMYGDALOIDE. (Fr.) } S1 ?? m -t>0&emia. 

The slaty or schistose phonolites are those which are 
most usually of tabular or columnar jointed structure. 
Those which are not slaty are usually only irregularly 
massive. 

This rock forms isolated conical hills, even more per- 
fectly than basalt, especially so in the Bohemian Mittel- 
gebirge and in the Oberlausitz. Much more rarely does 
it form great connected mountain ranges, and it is more 



GEANITIC GROUP. (2) PLUTONIC. 201 

rarely found in the form of dykes than basalt. On the 
continent of Europe, phonolite is only known as of ter- 
tiary or of still more recent origin, and never as a genuine 
plutonic rock. It is, on the other hand, also unknown as 
actual lava at active volcanoes, and from this it would 
appear that its state must be more or less the result of 
cooling under pressure or of transmutation. In favour of 
the latter supposition (of transmutation) is the presence 
of zeolite, which is, however, not a constant ingredient. 

Lyell, in his Geology, has instanced the occurrence of a 
phonolite of the Devonian period in Forfarshire. If this 
be a genuine phonolite, it is the only recorded instance of 
such being found of earlier than tertiary origin, but as 
the notice is quite incidental, and has reference to a 
different subject, and is moreover very brief, we can- 
not, without further explanation, accept it as authority 
in contravention of a law which otherwise appears uni- 
versal. 

References. 

Gmelin, in Poggend. Ann. 1828, vol. xiv. p. 259. 
Stntve, in Poggend. Ann. 1826, vol. vii. p. 348. 
Meyer, in Poggend. Ann. 1839, vol. xlvii. p. 192. 
Redtenbacher, in Poggend. Ann. 1839, vol. xlviii. p. 494. 
Schill, in G. Leonhard's Beitr. z. miner. Kenntn. von Baden, 

1854, vol. iii. p. 59. 
Schmid, in Poggend. Ann. 1853, vol. Ixxxix. p. 295 ; v. L. u. 

Br. Jahrb. 1856, p. 845. 
Jenzsch, in the Zeitschr. d. d. geol. Ges. 1856, p. 167 ; and 

Poggend. Ann. vol. xcix. p. 417. 
v. Rath, in the Zeitschr. d. d. geol. Ges. 1856, p. 291, and 1860, 

p. 29. 
Enqelbach, in the Erl. z. geogn. Karte v. Hessen, Sect. Schotten, 

1859, p. 45. 
Fischer, Die Trachyte u. Phonolithe des Hohganes, v. L. Jahrb. 

1862, p. 356. 
Rammekburg, Analysen von Phonolithen, Zeitschr. der d. geol. 

Ges. 1862, vol. xiv. p. 750. 

v. Fritsch has lately set up a distinction between nepheline- 
phonolite, nosean-phonolite, leucite-phonolite, and felspar- 
phonolite, Neues Jahrb. fur Mineral. 1865, p. 663. 

2. Plutonic. 

Granite is the principal rock of the plutonic division of 
the acidic igneous rocks, as trachyte is of the volcanic 
division of the same rocks. 



202 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

The other plutonic rocks rich in silica may all be classed 
with granite as subordinate varieties of the same com- 
pound. The principal of these are quartz-porphyry, 
felsite rock, and pitchstone, all of which may be almost 
regarded but as different states of the same substance, 
bearing somewhat the same relation to granite as the 
rhyolites to the trachytic rocks. We therefore describe 
them all as granitic igneous rocks, although the idea of 
a granular texture is usually conveyed by the name of 
granite. 

In the composition of all these rocks, orthoclase, or an 
orthoclastic substance, is predominant (frequently asso- 
ciated with other felspars), and is combined with quartz, 
mica, chlorite, talc, some hornblende, &c. ; never with 
augite. 

The various combinations of these mineral ingredients 
give the following specially named rocks each with their 
subordinate varieties. 

1. Granite. A compound of felspar, quartz, and mica ; 
granular, and sometimes also porphyritic, or other variety 
of texture. The following are varieties in composition : 
protogine, syenite-granite, schorl-granite, adularia-granite, 
granitite, ferruginous granite, graphite-granite, beresite, 
aplite. 

2. Granitic porphyry and (so-called) syenitic porphyry. 
A rock containing the same ingredients as granite. The 
matrix is usually compact, enclosing distinct crystals or 
grains of felspar, quartz, and mica, or chlorite. 

3. Quartz-porphyry. A compact matrix of the same 
chemical composition as granite, with separate individual 
crystals of felspar and quartz. 

4. Felsite rock, or petrosilex. The matrix of quartz- 
porphyry without its crystals. 

5. Pitchstone and pitchstone-porphyry. The same sub- 
stance as the above in a vitreous state, sometimes with 
crystals of felspar and quartz. 

It may appear to be inconsistent to treat the four last- 
mentioned rocks as distinct species, instead of mere varie- 
ties of the same species, as in the case of the rhyolites in 
the trachytic group. Our only reason for a different 
treatment is, that in general they are capable of being 
more easily distinguished from each other. 



GRANITIC GROUP. 203 

16. GRANITE. 

GRANIT. {Germ.) 
GRANITE. (Fr.) 

A crystalline granular compound of felspar, quartz, and 
mica. In certain varieties there occur chlorite, talc, 
hornblende, and schorl. 

Spec. grav. ...... 2-6 2-7 

Contains silica 62 81 p. c. 

The several mineral grains or particles are firmly knit 
together by their crystalline surfaces, without any uniting 
medium. They are of a size to be individually recognised, 
but their size is very various, and the rock is accordingly 
coarse-grained, fine-grained, or medium-grained. The so- 
called giant granites have grains larger than a walnut, 
other varieties not larger than mustard-seed. If the 
grains are so small as to become indistinct, and the rock 
assumes a compact texture, then it is no longer granite 
according to the usual meaning of the term. 

We shall treat of these compact states hereafter under 
the names of felsite rock and petrosilex ; they form states 
of transition between granite and other rocks. 

The felspar is usually the predominant ingredient, and 
the mica occupies the smallest place in granite. 

The felspar is chiefly orthoclase, very often accompanied 
by some oligoclase. Oligoclase alone has not yet been 
observed with certainty. It is also uncertain if albite or 
labradorite ever occur in the granitic compound. 

The orthoclase is somewhat various ; it is usually the 
common opaque species of yellowish-white or reddish 
colour ; more rarely grey or greenish. At many places 
(as, for instance, in the central chain of the Alps), it is 
principally that transparent vitreous variety, frequently 
split and cracked, which is termed adularia. The ortho- 
clase of granite is most readily to be distinguished from 
the oligoclase by its fresher state, its mother-of-pearl 
lustre, and simple twin growth ; whereas the oligoclase is 
somewhat of resinous lustre, and has delicate parallel 
stria? arising from multiform twin growths, or it is more 
decomposed, dull, paled in colour, or even transmuted 
into a totally different substance resembling steatite. 
Sometimes a thin coating of oligoclase is found incrusted 
round the grains of orthoclase. 



204 ACIDIC IGNEOUS ROCKS. (-2) PLUTONIC. 

Orthoclase not only occurs as an ingredient in the 
normal granitic compound, but sometimes prominently in 
distinct twin crystals imbedded in the granitic mass, in 
which case the rock is termed porphyritic granite. These 
crystals are sometimes several inches long, and they enclose 
particles of quartz and mica, so as to form inside the crystal 
small kernels or parallel streaks of fine-grained granite. In 
the granite of the Fichtelgebirge, very large twin crystals 
of orthoclase are sometimes found broken, their several 
parts lying imbedded close together, just as in the case 
of the sanidine crystals of the Drachenfels trachyte. 

The quartz in granite is seldom in the form of perfect 
crystals ; it usually forms grains of irregular shape, or 
masses grown in with the other mineral ingredients of the 
granite, chiefly with the felspar. It is tolerably trans- 
parent and colourless or white, dark-grey, vitreous, most 
easily recognisable by its hardness. The granite of Rum- 
burg in Bohemia contains a dark-blue variety of quartz. 
It is remarkable that this, the most difficult of fusion of 
all the ingredients of granite, is often found hemmed in 
between the felspar and mica, and to have received impres- 
sions from the felspar at least ; whence it follows that the 
quartz must have solidified somewhat later than it. 

The mica of granite occurs in the form of thin laminae 
or small hexagonal plates, whose cleavage-planes lie in 
various directions, and therefore do not occasion a foliated 
texture. Sometimes they are clustered in small bunches ; 
or sometimes long continuous rays of mica run through 
the whole rock. Most usually it is potash-mica or mag- 
nesia-mica ; sometimes margarodite ; or lithia-mica, white, 
grey, brown, black, more rarely yellow or green in colour. 
Occasionally different coloured micas occur in the same 
rock, or a narrow border of white potash-mica envelopes 
the dark magnesia mica. But it is often difficult accu- 
rately to determine the species of mica in these thin laminae ; 
the easiest test is generally the optical. It is worthy of 
remark that potash-mica and tourmaline (schorl) appear 
only to occur (as original products) in plutonic-igneous 
or metamorphic rocks, and in plutonic dyke formations ; 
never in volcanic rocks. 

The ingredients which we consider as essential for 
granite are nevertheless sometimes replaced by others. 



GRANITIC GROUP. 20,5 

This species of substitution occasions varieties in composi- 
tion which will be more particularly described below. It 
occurs especially with the mica, whose substitutes are, talc, 
chlorite (in protogine), schorl (in schorl-granite), graphite 
(in graphite-granite), micaceous iron (ferruginous granite). 

Sometimes a fourth ingredient appears in local but 
characteristic varieties of granite; e.g. hornblende (in 
syenitic granite) or pyrites (in beresite). 

The following minerals occasionally occur in granite, 
but only as accessories ; viz., tourmaline, garnet (always in 
the form of trapezohedra), andalusite, topaz, beryl, pinite, 
apatite, fluorspar, pistacite, corundum, zircon, titanite, 
gadolinite, orthite, pyrorthite, allanite, cordierite, magnetic 
iron-ore, tin-ore, mispickel, molybdenite, and native gold. 

We find many transitions from granite into other rocks. 
These are partly occasioned by variations of composition, 
and partly- by variations of texture. The accession of 
talc, chorite, schorl, or hornblende to the granitic com- 
pound occasions transitions into protogine, schorl rock, or 
syenite. If the felspar of granite disappears, we obtain 
gr lessen, or if the quartz disappears, mica-trap (minette), 
or if the mica disappears, aplite, and a kind of granulite. 
If the laminae of mica assume a parallel direction, then the 
texture becomes foliated, and gneiss is the result. If the 
matrix of a porphyritic granite becomes very fine-grained 
to compact, then we have a transition to granitic porphyry ; 
and if in that case the mica also disappears, then the rock 
becomes quartz-porphyry. Finally, if the whole granitic 
compound becomes very fine-grained to compact, then the 
rock isfelstone. 

Varieties in Texture. 

(a) COMMON GRANITE. \ Coarse, medium, or fine-grained, pro- 
GEMEiNERGRANrr.^rro.) f bably the most extensively diffused of 

GBAKTTE COMMUN. (/*.) J ^ ^^ ^ j f ^ ^^ ^ 

very coarse, it is sometimes called giant granite. Trebendorf, near 
Eger. Very fine-grained varieties, on the other hand, occur at 
Kerbersdorf, near Eger, in Bohemia, at Welsau, near Redwitz, and 
in the Vienna paving-stone. 

(6) PORPHYRITIC GRANITE. \ The porphyritic texture is usually 

GEBIROS-GRAIOT, r. Leonhard. I caused by large orthoclase crys- 

G JS^RPHTRotoE. (Fr.) I tals, more rarely by quartz crys- 

' tals. The principal mass is 

granular. Carlsbad and Ellenbogen, Ochsenkopf and Gop- 
fersgriin in the Fichtelgebirge, &c. As a subvariety of this 
class, we may cite the rappakivi of Finland, the principal mass 



206 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

of which is usually much decomposed ; it encloses rounded masses 
of red felspar often half an inch across, enclosed by orbicular 
envelopes of green oligoclase a quarter of an inch in diameter. 

(c) GKEISSIC GRANITE. | A granite with foliated texture. In 

GNEISSGRANIT. (Germ.) L a geological point of view, much of 
GRANITE GNEISSIQUE. (Fr.) ) what ^tterly has been called red 

gneiss (gneissite), and which appears to be eruptive, must be 
here included. Perhaps some grey gneiss too. 

(d) GRAPHIC GRANITE. j The orthoclase is altogether predomi- 

SCHRIFTGRANIT. (Germ.) L nant in large crystals, and is penetrated 
GRANJTEGRAPHIQUE.OPV.) * Iccording to a singular 



PECHMATIT, Naumann. 

(Germ.) 
PEGMATITE, ffaily. (Fr.) 



crystallographic law, so that in certain cleavage-planes it pro- 
duces figures resembling writing. The mica (usually white) is 
accumulated separately in groups. This remarkable variety 
usually only forms subordinate masses or dykes of small extent 
in the ordinary granite or in gneiss or mica-schist, but such 
dykes' are very frequent, e. g. in the Schloitzbachthal, near 
Tharand, in Saxony. 

(e) PEGMATITE. \ This rock Naumann separates from the 

graphic granite, and he understands by 
it a variety, very coarsely and irregu- 
> larly constituted, of orthoclase, quartz, 
and silvery-white mica. It often contains tourmaline, and 
occurs under the same conditions as the graphic granite, and 
frequently together with it. 

This seems the proper place for certain other granites of 
irregular composition very rich in felspar. Some are traversed 
by dark continuous rays of mica, in others the felspar assumes 
a form resembling flowering stalks (Blumengranif). 

In the granite of Ballybrack, near Dublin, the mica (Marga- 
rodite) assumes this plumose form, occurring in branches of 
Prince of Wales' feathers, one inch across and several inches 
long. Jukes. 

The granites of this class are all of very small extent, and 

their particular character is probably owing to special circum- 

stances. They all usually contain many accessory minerals, such 

as albite, tourmaline, topaz, beryl, garnet, gadolinite, orthite, &c. 

They are sometimes so imbedded between strata of crystalline 

schist that they can scarcely be regarded as of eruptive origin. 

(/) MIAROLITE. \ Is the name given by Fournet to 

MIAROLITH. (Germ.) > a o-eodic granite, rich in oligoclase, 

MIAROLITE, Fournet. (Fr.) J in " tlie nei | hbour h ood o f Lyons, and 

at Baveno in the Alps. 

The following are varieties in composition ; in them 

we find many of the varieties in texture repeated. 

(</) PROTOGINE. ] A granite which contains talc or chlorite 

PROTOGIN. (Germ.) L or decomposed mica instead of the usual 

pROTOGi*E,/ M rm*. (Fr.)] ^^ li{& yery extensively developed 

in the Western Alps. In the Erzgebirge much of the granite 
lying between Schneeberg and Eibenstock contains no mica, but 
in its stead siskin-green talc, which combined with flesh-red 
felspar and white quartz gives that rock a singular appearance. 



GRANITIC GROUP. -207 

(h) SYENITIC GRANITE, granite with hornblende. If the quartz and 
mica gradually diminish and finally disappear from the granitic 
compound, then the rock passes over into a syenite. Syenitic 
granite is often porphyritic, owing to the presence of large 
crystals of orthoclase. It is very abundant near Moritzburg 
and Meissen, in Saxony. The greater part of what is usually 
called syenite properly belongs to this class, especially those 
syenites which contain quartz or mica as characteristic in- 
gredients. But there is no definite boundary between syenitic 
granite and syenite. 

(i) SCHORLACEOUS GRANITE. } Granite with schorl in the place of mica, 
ScHORLGRAxrr. (Germ.) L usually fine-grained, and forms veins in 
LUXULUAMTE, Pitani. { Qther ^^ ^ for ' in8tance , near Hei- 
delberg and near Predazzo in Tyrol (very characteristic) : the 
latter is a compound of orthoclase, quartz, and schorl. 

The name Luxullianite has been proposed by M. Pisani for a 
porphyroidal granite, in which thfi~ mica is replaced by tour- 
maline/ because it is found in the parish of Luxullian,' in Corn- 
wall. 

() ADULARIA GRANITE and ADTJLARIA PROTOGINE. > With adularia 

ADULARGRANIT und ADULARPROTOGIN. (Germ.) I in the place of 

the ordinary felspar ; very extensively developed in the Alps. 

(1) GRANITITE. ' ) Is the name proposed by G. Rose for all 

GRAxrnr. (Germ.) \ granites containing much oligoclase with 

red orthoclase, quartz, blackish-green magnesia-mica in small 

quantity, and no white mica. This rock forms the principal 

material of the Riesen Gebirge; it occurs in the Brocken of 

the Hartz Mountains, Brixen in the Tyrol, &c. In composition 

it is identical with the mariolite of Foumet. 

(m) RTJMBURG GRANITE. > With blue quartz, occurs at Rum- 
RUMBURGER GRAuiT. (Germ.) \ burg in Bohemia, also at Pic Blanc 
in the Monte Rosa chain, 
(n) GRAPHITIC GRANITE. > With graphite in the place of mica, 

GRAPHITGRANIT. (Germ.) \ e . g. near Passau, on the Danube. 
(0) FERRUGINOUS GRANITE. ) With micaceous iron instead of the 
EISKNGRAXIT. (Germ.) \ ordinary mica. Occurs at several places 
in the Fichtelgebirge, also in iron-mines near Dossenheim in 
the Odenwald. 

(p) BERESITE. ) A granite containing pyrites and very little 

BERESTT. (Germ.) \ niica ; forms considerable dykes in the clay- 
slate near Beresowsk in the Ural. These dykes are themselves 
traversed by quartz veins containing gold. 

(q) APLITE or SEMI-GRANITE. ^ Is the name given to a variety 

APLTT oder HALBGRANTT. (Germ.) } O f very subordinate extent, 
consisting only of quartz and orthoclase, and therefore mine- 
ralogically allied to granitite. 

GREISEN might also be reckoned as a variety of granite without 
felspar. It does actually pass over into granite. . Its special 
geological character seems, however, to entitle it to be men- 
tioned as a separate rock. (See post, No. 50.) 

(r) TONALITE. ) The name given by Vom Rath to the 

TONALTT, Foro Rath. (Germ.) I roc k which forms the principal mass 

of the Adamello group of mountains in Southern Tyrol, and 



208 ACIDIC IGNEOUS EOCKS. (2) PLUTONIC. 

which has hitherto always been described as granite. It is a 
crystalline granular compound of triclinic felspar with quartz, 
magnesia-mica, and hornblende. The triclinic felspar belongs 
to an entirely new species not yet named. The quartz forms 
at least one-third of the whole mass. It contains as accessories, 
orthoclase, orthite, titanite, and magnetic iron-ore. It contains 
67 per cent, of silica. Many dark-coloured concretions are 
contained in the rock. In Tyrol this rock has broken through 
the mica-schist. (Zeitschr. d. deutsch. geol. Ges. 1864, p. 249.) 

All the varieties of granite are most commonly of irre- 
gularly massive or else of thick tabular jointed structure. 
By weathering, elliptical bodies are sometimes formed 
which fall off in concentric layers, the interior remaining 
fresh and firm. Granite is often found in large blocks 
and boulders on the surface of the ground. 

Granite is unquestionably one of the most extensively 
prevalent of rocks, and its mineral compound, which is 
also that of gneiss, is without doubt the most important 
and frequent of all the rock substances of the earth. 
Moreover, we find granite in all regions of the globe 
assume the same or analogous bedding in relation to 
other rocks. It frequently occupies extensive tracts, and 
sometimes forms the backbone of whole mountain re- 
gions. It also frequently forms dykes, and these some- 
times penetrate the larger granite masses (from which 
they may be distinguished by their texture) ; sometimes 
the crystalline schists or older sedimentary formations : 
granite dykes having been exceptionally found as late as 
the Jurassic formations, e. g. in the Alps. The greater 
part of the granites accessible to observation appear, 
however, to be older than the coal formation, and to be 
of deep plutonic origin. These granitic dykes are occa- 
sionally accompanied by so-called contact formations ; 
such as friction breccias ; silicification of the neighbouring 
rock ; chiastolite-schist ; nodular schist (see post, p. 257) ; 
granulation of limestone, &c. 

The usual bedding* of granite, and its relation to the 
bedding of adjoining rocks, unmistakably prove its erup- 
tive character, except, perhaps, in some special cases. 
Some doubts, however, which deserve our notice, have 
been raised as to its former state of igneous fusion. 

* The term ' bedding ' applied to igneous rocks, especially to granitic 
rocks, must be taken as equivalent to ' mode of occurrence ;' and l erup- 
tive' as only meaning 'intrusive' or 'irruptive.' TRANSLATOR. 



GEAXITIC GROUP. 209 

These rest chiefly upon the fact of the quartz having 
solidified later than the felspar and mica, and on the want 
of distinct traces of the effect of heat on the rocks which 
the granite appears to have broken through. These ob- 
jections, it appears to us, may be satisfactorily answered 
by supposing the granite always to have consolidated at 
great depth, and under genuine plutonic influences, per- 
haps even with the aid of water. The great resemblance 
which granite bears to the trachytic rocks speaks, at all 
events, for a similar process of formation for both. 

That there are no new granites of volcanic origin is a 
necessary consequence of the assumed fact that the granitic 
compound can only have originated in the depths of the 
earth. We must likewise assume that great periods have 
elapsed in every instance from the time of the formation 
of granite rocks before they have become exposed to view. 
We may well assume that the trachytes represent the vol- 
canic part of the same igneous formation which gave birth 
to the granites. 

The name of granite (according to Emmerling's Lehrb. 
d. Mineralogie) was first applied to rocks by Tournefort 
in the year 1698. But according to Breislack's Lehrb. 
d. Geologic, it had been used by Caesalpinus as early as 
1596. For a long time it was, doubtless, used to desig- 
nate every coarse-grained compound rock. The meaning 
of the term was first more definitely fixed by Werner. 
It has from the first been felt to be a geological necessity 
to group with granite many other rocks bearing a close 
affinity to it, but it has always been no less difficult to say 
where the line should be drawn. 

In 1849, G. Hose proposed the following new division 
and grouping of granitic rocks (see Zeitschr. d. d. geol. 
Ges. p. 352) :- 

1. Granite (proper), essentially consisting of orthoclase, white (potash-) 

mica, black (magnesia-) mica, and oligoclase ; as accessories, 
hornblende, orthite, titanite, apatite, and iron pyrites. 

2. Granitite, essentially consisting of orthoclase, oligoclase, quartz, 

and magnesia-mica ; as accessories, hornblende, orthite, zircon, 
titanite, pyrites, chalcopyrite, and molybdenite. 

Now as Rose himself subdivides his granite (proper) into 
several varieties whose composition differs as much from each 
other as granitite from granite, no sufficient reason appears for 
this violent division and new nomenclature. 

3. Syenite, essentially consisting of orthoclase, oligoclase, hornblende, 

P 



210 ACIDIC IGNEOUS EOCKS. (2) PLUTONIC. 

magnesia-mica, and quartz ; as accessories, titanite, apatite, 
magnetic iron-ore, &c. 

The difference "between this and the granitite also consists in 
the greater frequency of the hornblende, in its being named as 
an essential instead of an accessory ingredient. This is our 
syenitic granite. The genuine syenite of the Plauenschen- 
Grund does not agree with this definition because it seldom 
contains mica and, perhaps, contains no quartz at all. There- 
fore Rose sets up varieties of composition differing, however, 
more from each other than his syenite from granite. 

4. Porphyry, essentially consisting of orthoclase, oligoclase, quartz, 

and magnesia-mica; as accessories, cordierite, garnet, ortliite, 
and pyrites, its essential difference from his granite or granitite 
consisting only in texture. 

Now, as oligoclase and mica entirely fail in many rocks which 
Hose reckons as porphyries, he has been driven again to make 
varieties which differ almost more from each other than his 
porphyries from the other granitic rocks. 

5. Syenitic Porphyry, with a matrix enclosing crystals of orthoclase, 

oligoclase, magnesia-mica, and hornblende; as accessories, 
garnet, nepheline, titanite, quartz, magnetic iron-ore, specular 
iron, and pyrites. 

This is a very different rock from that which has received 
the name of syenitic porphyry ever since Werner's time. It is 
our porphyrite, which as we have seen may be divided into (A) 
a rock essentially felspathic, (B) containing felspar and horn- 
blende, and (C) containing felspar and mica. 

The literature respecting granite is, as we might ex- 
pect, a very rich one we will only cite a few treatises 
on the more special phenomena. 

References. 

G. Rose, On the Granitite of the Riesengebirge, Zeitschr. d. d. 
geol. Ges. 1857, p. 513. 

Cotta, On the Rumburg Granite with blue Quartz. Erlauter. z. 
geogn. Karte v. Sachsen, 1839, No. 3, p. 14. 

Four-net, On Miarolit, Mem. sur la Geol. des Alpes, part. 2, p. 24, 
and Bullet, de la Soc.^ geol., [2] vol. ii. p. 495. 

Sothlinkff, On Rappakivi a granite which,' however, often 
contains no quartz, and then is very similar to mica-trap, v. 
L. u. Br. Jahrb. 1840, p. 613. 

v. Rosthorn and Canavd, On Albite-granite and Tourmalin- 
granite in the Alps. v. L. u. Br. Jahrb. 1855, p. 584. 

v. Richthofen, On Granitite, Tourmalin-granite, and Tourmalin- 
syenite, Geogri. Beschr. von Siid-Tyrol, 1860, pp. 108 and 
148. 

Axel- Gadolin distinguished two kinds of granite dykes in the 
gneiss of Ladoga Lake, viz. : older dykes, with albite from 
two of more recent formation, containing much oligoclase. 
Verhandl. der k. russ. mineral. Ges. zu Petersburg, 1857-8, 
p. 85. 



GRANITIC GROUP. 211 

Svanberg comes to the conclusion from analysis that besides 
orthoclase other orthoclastic felspars occur in granite. Journ. 
f. prakt. Chem. 1844, vol. xxxi. p. 161. 

I)('l<-sse distinguishes in the Vosges Mountains protogine from 
'(iranite sye*nitique des Ballons.' Bullet.de la Soc. ge*ol. 
1852, [2] vol. xi. p. 464. 

Also, ' Granite des Ballons,' ' Granites des Vosges/ and 
' Filons de Granite.' Ann. des Mines [5] vol. jii. p. 369. 

On the Pegmatite with Tourmalin of Saint Etienne in the 
Vosges. Ann. des Mines, 1849, [4] vol. xvi. On Pegmatite 
of Ireland. Bullet, de la Soc. g(ol. 1853 [2] vol. x. p. 568. 

Haw/hlon, Quart. Journ. Geol. Soc. 1856, vol. xii. p. 177 ; 
and 1858, vol. xiv. p. 300. Address delivered before the 
Geol. Soc. of Dublin, 1862. 

.R. Scott, The Granites of Donegal. Journ. of the Geol. Soc. 
of Dublin, vol. ix. p. 285. 

Scheerer, Granite Tyrols. Jahrb.'f. Min. 1864, p. 385. 

Sir W. E. Logan, Classification of Eruptive Rocks. Rep. 
Geol. Surv. Canada to 1863, p. 645. 

G. LconJiard distinguishes between older and newer granite 
veins in the Heidelberg mountain granite. Gegend um 
Heidelberg, 1844. 

Bunsen, On Granite formation. Zeitschr. d. d. geol. Ges. 
1861, p. 96. 

C. Rothe, iiber die krystallinischen Gesteine des Ries. Jahrb. 
fiir Mineralogie, 1863, p. 169, contains many new analyses 
of granite. 

v. Helmersen has described the Rappakivi of Finland, of which 
the Alexander column of St. Petersburg is formed, as a por- 
phyritic granite with a flesh-red felspar predominant. 

n/8on treats of the supposed neptunic origin of granite in the 
Edinb. New Philos. Journal, 1861, vol. xiv. p. 149. 

Fuchs on the granite of the Ilartz in the Jahrb. fiir Mineralo- 
gie, 1862, pp. 769, 807. 

H. C. Sorby. On the Microscopical Structure of Mount Sorrel 
Granite : Proc. Geol. and Polytech. Soc. W. Riding of 
Yorksh., 1863-4, pp. 301-4. On "the Microscopical Structure 
of Crystals, indicating the Origin of Minerals and Rocks : 
Quart. Journ. Geol. Soc. 1858, vol. xiv. p. 453. 

Sorby and (later) Zirkel have made interesting dis- 
coveries by microscopic analysis of granites and several 
other igneous rocks. 

The quartz and the felspar of Granite are found to en- 
close numerous very small vesicles filled with water and 
air, and also many minute particles of glass. The quartz 
also contains some very minute crystals of felspar. The mi- 
croscopic structure of the Trachytes very closely resembles 
that of the granites ; their compact matrix Zirkel recog- 
nised as a compound of felspar and quartz. In the compact 
mass of fresh Basalt he recognised a compound of felspar 

p 2 



212 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

and magnetic iron-ore with very Mttle olivine, and traces 
only of augite. The vitreous mass of Pitchstone resolved 
itself under the microscope into a confused compound of 
very delicate acicular crystals. The same thing with 
Obsidian. Even the newest Lavas exhibited in their 
mass very minute pores filled with water. 

17. GRANITIC PORPHYRY and SYENITIC 
PORPHYRY. 

GKANITPORPHYR und SYENTTPORPHYR. (Germ.} 
A compact or fine-grained felsitic base, enclosing crystals 

or crystalline grains of felspar, quartz, and mica, or 

chlorite. 

Spec. grav. < . . Y , . . 2-6 27 
Contains silica , . . . . 61 64 p. c. 

The matrix is yellowish, brownish, or dark green. 
When not quite compact, its material may be recognised 
as consisting principally of felspar, combined with quartz, 
mica, or chlorite in small proportion. The presence of 
chlorite occasions transitions into porphyritic granite or 
protogine ; but in distinguishing and naming these transi- 
tion rocks, their geological relations must always, to some 
extent, be taken into account. 

The distinct crystals of felspar are very numerous in 
this rock, and are usually of large size. They are for the 
most part twin crystals of orthoclase, and these are often 
coated with a different species of felspar, probably oligo- 
clase, crystallographically combined (grown together) with 
the orthoclase. There sometimes occur also separate and 
smaller felspar crystals and grains ; these latter, as well as 
the crust of the larger crystals, show delicate stripings, 
and therefore both, probably, consist of oligoclase. 

The quartz most usually forms small grains or crystals 
of a smoke-grey colour, often, however, larger diplohe- 
drons (which were formerly mistaken for double pyramids) 
very distinct and prominent. 

The dark mica usually only occurs in small delicate 
flakes or thin hexagonal plates. If the rock contains 
chlorite instead of mica, as in the variety termed syenitic 
porphyry, the chlorite forms small dark green scaly grains, 
or else it is intimately blended with the matrix, to which 
it imparts a green colour. 



GKANITIC GROUP. 213 

The above-mentioned modifications give rise to several 
varieties of the rock. 

Varieties in Texture. 

(a) COMMON GRANITE-PORPHYRY. The matrix is compact through- 

out ; often dark-coloured. It contains separate crystals, grains, 
or laminae of orthoclase (and sometimes oligoclase), quartz, 
and mica. If the mica faiis ; the rock passes into ordinary 
quartz-porphyry. Frequent in the Thuringian Forest, e.g. 
near Schmiedefeld, and in the Drusenthal, where it forms dykes 
of great thickness. 

(b) GRANITIC GRANITE-PORPHYRY. i The matrix resembles 

GiiAxn-AHNLicHER GRANITPORPHYK. (Germ.) I" j n part a fine-grained 
granite, but distinct crystals of orthoclase, and large grains of 
quartz, and also laminae of mica, are separately and prominently 
developed. Frequent in the neighbourhood of Schellerhau and 
Biirenburg in the Erzgebirge. The composition of this rock is 
very similar to that of porphyritic granite. The geological 
character in these doubtful cases should determine the nomen- 
clature of each particular rock. 

At Niederschona, near Freiberg, where a rock belonging to 
this class forms a vein in gneiss, it contains large light- 
coloured twin crystals of orthoclase, whose exterior appears fresh, 
but inside each crystal is a decomposed nucleus frequently 
changed into a greenish substance like lithomarge. It would 
almost seem as if the nucleus of the orthoclase crystal had 
originally consisted of oligoclase or a compound of oligoclase 
and quartz. The magnificent columnar granite-porphyry of 
Altenhain, near Frankenberg, in the Erzgebirge, is a rock of the 
same class, but the orthoclase crystals do not exhibit the same 
phenomenon as those of Niederschona. 

Near Liebenstein in the Thuringian Forest, a granitic 
porphyry traverses and forms dykes in the ordinary granite. 
It possesses a very fine granitic matrix, and very distinct 
white crystals of orthoclase, with brown edges ; also dark spots 
or fragments (which are still compact) of greenstone which 
the porphyry has broken through. 

(c) MICACEOUS GRANITE-PORPHYRY. \ This rock, which Kit- 

GUMMERREICHER GRANTTPORPHYR. (Germ.) } tel first described under 
the name of granitic porphyry, and which occurs at Aschaffen- 
burg, interposed between syenite rocks, consists of a fine-grained 
to compact felsitic mass rich in mica (a kind of minette) in 
which numerous grains or crystals of quartz and somewhat 
fewer, but much larger crystals of felspar are imbedded. 
According to Kittel, the quartz crystals often show prismatic 
surfaces. The orthoclase crystals are partly single, partly 
twins, very fresh, without marginal crust, and have well-defined 
edges, but strange to say, completely rounded off, so that their 
cross-section always appears elliptical. 

(d) CHLORITIC GRANITE-PORPHYRY. \ Often called syenitic por- 

GRANrmjRpHYR. (Germ.) ) phyry, probably because 



214 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

the. particles of chlorite which it contains have been mis- 
taken for hornblende ; but in some places the rock appears 
actually to contain some hornblende as an accessory. The 
matrix is compact or fine-grained, .brown or dark green, 
often very rich in quartz, and contains chlorite, and some- 
times mica also. The chlorite forms little flakes or grains, 
the quartz is in the form of diplohedrons, and the twin 
crystals of orthoclase are sometimes more than an inch long. 
In the syenitic porphyries of the Erzgebirge (the rocks ori- 
ginally so named by Werner) these orthoclase crystals are often 
enveloped in an outer coating of oligoclase, of about one-tenth 
of an inch thick, showing distinct twin stripings. The oli- 
goclase is sometimes lighter in colour than the orthoclase 
(greenish-yellow) sometimes darker (brown), and it is gene- 
rally more decomposed than it. This rock near Frauenstein 
and Altenberg has broken through gneiss, mica-schist, granite, 
and quartz-porphyry, and forms very important and extensive 
dykes in those rocks many miles in length. Near Frauenstein 
it contains, according to Rube, about 64 p. c. of silica. 

Naumann has described a rock of somewhat different cha- 
racter under the name of green porphyry. It occurs in the 
neighbourhood of Wurzen in Saxony, where it forms small 
rocky hills. Its matrix is dark-green, probably from chlorite, 
and it also contains some magnetic iron-ore. 

Dr. Rube determined its proportion of silica at about 61 p. c. 
This rock is likewise more recent than the quartz-porphyry of 
the same district. 

(<?) THE BASE or MOTHER ROCK of these Porphyries occasionally 
occurs free from crystals (towards the outer margin of the 
rock), and it then assumes very much the character of a fine- 
grained granite, poor in mica and rich in chlorite. 

All the above-named varieties are most usually massive, 
but sometimes of columnar-jointed structure. They form 
great mountain masses or thick dykes. There are no 
vesicular or amygdaloidal varieties, or tufa formations of 
rocks belonging to this group. 

References. 

Zirkel, Geogn. Verh. d. Umg. von Aschaflfenburg, 1840, p. 30. 
Naumann. Erlauter. zur geogn. Karte von Sachsen, 1836, No. 1, 
p. 139. 

18. QUARTZ-POKPHYKY, ELVANITE. 

QUARZPORPHYR. (Germ.} 

PORPHYRE QUARTZIFERE, ELVAN". (Fr.) 

A compact felsitic mass as matrix, enclosing crystals or 
crystalline grains of felspar and quartz. 

Spec, grav 2 -5 2 -6 

Contains silica ..... 70 81 p. c. 



GRANITIC GROUP. 215 

The compact matrix of the quartz- porphyries consists 
principally, if not altogether, of felspar ; this is sufficiently 
proved by its hardness, weight, colour, as well as by 
chemical analysis; and from its compactness, its large 
proportion of silica and the crystals of orthoclase which are 
imbedded in it, we conclude that it most probably consists 
of orthoclase. Its proportion of silica is, however, too high 
even for orthoclase, and it is therefore probable that some 
quartz is intimately combined with the felspar. If this 
be the case, it would not alter the fusibility of the rock 
before the blowpipe. An intimate compound of felspar 
and quartz melts almost as readily as felspar alone. The 
colour of the matrix generally varies between yellowish 
and reddish, but sometimes goes over into brown and 
grey, and even to white. Exceptionally, also, violet and 
green varieties occur. 

The state or texture of the matrix varies somewhat, 
and the differences are partly original, partly occasioned 
by decomposition and weathering. Sometimes it is quite 
compact like hornstone, with a smooth conchoidal frac- 
ture ; most usually it is compact with uneven dull fracture, 
which appears to be the sign of transition towards a crys- 
talline state ; finally, it is sometimes rough and dull, 
almost earthy, which is a sign of commencing decompo- 
sition (kaolinising of the felspar). Owing to these dif- 
ferences of texture or state, the substance of the rock 
itself was formerly regarded as varying essentially, and it 
has been so described, whence the names of hornstone- 
porphyry, felstone-porphyry, and clay stone-porphyry, or 
even clay-porphyry. The differences, no doubt, exist, 
but they are only of a different arrangement of particles, 
or of decomposition of one and the same substance. This 
matrix of the quartz-porphyries, which sometimes occurs 
as a separate rock without crystals, has received separate 
names, such zsfelsite or felsite rock, eurite, petrosilex, and 
halleflinta, hence also the names of felsite-pcrphyry and 
curite-porphyry. It is seldom or never of vesicular or 
amygdaloidal texture. 

In genuine quartz-porphyry, felspar and quartz are 
the only crystals which are porphyritically developed. 
If mica or chlorite occur in addition they constitute a 
transition into granitic porphyry. The felspar is usually 



216 ACIDIC IGNEOUS KOCKS. (2) PLUTONIC. 

orthoclase, and from its twin growth is usually very dis- 
tinctly to be recognised ; sometimes, also, oligoclase or 
sanidine occur. All these felspars where they occur por- 
phyritically are very distinctly and sharply developed, 
and are easily distinguished from the matrix. 

The crystals of quartz are white, grey, or almost black, 
but withal frequently transparent ; they are small, seldom 
larger than the size of a pea; they form either sharp- 
edged diplohedrons (without a trace of prismatic surface), 
or they are more or less rounded off at the edges and 
angles, or finally they form mere rounded grains without 
crystal surfaces. The rounding of these crystals is some- 
times so remarkable that it has given rise to the idea of 
their having been actually rounded by friction, which in 
genuine porphyries can hardly be the case. The number 
and proportion of the quartz crystals contained in the 
matrix, as also that of the felspar crystals, is very variable, 
and sometimes diminishes even to total disappearance, so 
that transitions take place into the quartzless-porphyrite or 
into felsite rock ; but quartz-porphyry, although poor in 
quartz, is nevertheless always to be distinguished from 
genuine porphyrite by its far greater proportion of silica. 
The quartz-porphyries on an average have more silica 
even than the granite, just as the rhyolitic division of the 
trachytes contains more silica than the trachytic. There 
is scarcely any petrographic difference between many 
quartz-porphyries (especially if they contain sanidine or 
oligoclase) and some kinds of trachyte-porphyry. They 
are sometimes so much alike as not to be distinguished 
from each other in ordinary hand specimens. In such 
cases the character of a given rock can only be determined 
geologically, and ascribed to the granitic or the trachytic 
group respectively, according as it occurs in a granite or 
trachyte district, or from its relation to some rock of more 
distinct character to which it may be traced by transitions. 

Smaller crystals or particles of quartz, but large enough 
to be discovered by the eye or with an ordinary lens, are 
often interspersed in the matrix between the larger and 
more distinct crystals of this rock. 

The quartz-porphyries seldom contain any accessory 
ingredients properly so called, and where such do occur 
they are probably only of secondary origin, products of 



GRANITIC GROUP. 217 

transformation, or new formation ; thus, for instance, pinite, 
talc, lithomarge, chlorite, pinguite, pyrites, and specular 
iron. But in veins or in clefts, nests or concretions in 
the rock, many minerals are frequently found, such for 
instance as quartz, hornstone, chalcedony, agate, opal, 
lithomarge, calc-spar, brown-spar, fluor-spar, barytes, 
specular iron, and dendritic pencilling^ of oxides of iron 
and manganese all which appear to be secondary for- 
mations caused by secretion from the rock's mass, or by 
infiltrated solutions. 

The porphyritic texture of the rock is sometimes united 
witli a fissile or fine laminated structure (riband-porphyry, 
band-porphyry) ; also sometimes- with geodic structure 
(millstone-porphyry), or else with spotted texture or there 
lie dispersed through the rock's mass smaller or larger 
felsite balls (pyromeride). 

Varieties in Texture. 
(a) COMMON QUARTZ-PORPHYRY. \ with compact ma trix and 

( : KM KIXER QUARZPOUPHYR. (Germ.) I 1 _ rai . p i fl n f fplqnnr onH niinrfy 

PORPHYKE QUARTZIKEHE coMMux. (/v.) ) crystals oi .ispar ana quartz. 
() Hornstone-porphyry (Homsteiuporphyr, Germ.\ Elvan, 



(j3) Felstone-porphyry (Feldsteinporphyr, Germ, j Pe*trosilex, 

JFK). 
(y) Clay stone-porphyry or Argittophry (Thonsteinporphyr 

oder Thonporphyr, Germ. ; Argtlophyre, Fr.). 
All frequent, in the Thuringian Forest and near 

Meissen, and near Tharand in Saxony. 



(6) STRIPED PORPHYRY (SLATY 
PORPHYRY). 

SCHIEFRIGER PORPHYR, SCHALEX- 

oder BAXDPORPUYR. (Germ.) 
PETROSILEX RUBANE. (Fr.) 



Composed of thin layers of 
somewhat dissimilar texture or 
colour; hence the fracture ap- 
pears to be striped like a riband, 
and the rock splits more easily 

in the direction of the layers than straight across. The layers 

are often much bent and twisted. Mohorn near Freiherg ; 

Winterstein in the Thuringian Forest, Wachenberg in the Oden- 

wald. 

(c) SPOTTED PORPHYRY. I Contains worm-shaped spots of dif- 

FLECKENPORPHYR. (Germ.) > ferent colour and texture from the 
matrix. This variety has also been called Kattun-porphyry. 
Leukersdorf near Chemnitz, Saxony. 

(d) POROUS, CAVERNOUS, OR ] A rock penetrated by numerous 

MILLSTONE PORPHYRY. I small irregular cavities or geodes, 
POROSER, DRUSIGER, oderMt^Hi^ f which are seldom vesicular, more 

STEINPORPHYR. (Germ.) ) usuftlly the regult of weathering> 

Tannebergsthal in the Erzgebirge, Regenberg near Frie- 
drichsroda, in the Thuringian Forest, where it is combined with 
pyromeride. 



218 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 



This rock in addition to the 
usual quartz crystals, contains 
balls of felsite (either small 



(e) PYROMERIDE (BALL-PORPHYRY).' 

KUGELPORPHYR oder PYROMERID. 

(Germ.) 
PYROMERIDE, Monteiro. (Fr.) 

' and numerous, or large and 

isolated. The small balls are frequently marked internally 
with radial streaks. The interiors of the larger ones are usually 
split after the manner of septaria, or they contain a geodic 
cavity. The clefts or cavities in the balls are wholly or 
partly filled with hornstone, chalcedony, agate, quartz, ame- 
thyst, calc-spar, fluor-spar, micaceous iron, &c. These balls, as 
we have already mentioned, frequently occur in combination 
with a geodic structure of the matrix. Regenberg and Schnee- 
kopf in the Thuringian Forest, the island of Corsica. 
(/) PORPHYRY WITH ] Forms a transition into felsite rock 
FEW CRYSTALS. I (petrosilex) or into porphyrite. The 
KRYSTALLARMER POR- f matrix alone, without crystals, is some- 
CYR. (Germ.) ) timeg foimd towar( J s tne o uter mar gi n o f 

masses of very distinct quartz-porphyries thus e.g. at the 
Weissritz, close above Dippoldiswalde in Saxony, The Frei- 
berg porphyry dykes are also mostly very poor in crystals of 
felspar and quartz, but they often contain, in their stead, small 
cubic crystals of pyrites. 

Varieties in Composition. 

(</) ORTHOCLASE-QTJARTZ-PORPHYRY. ^With orthoclase and quartz 
ORTHOKLAS-QUARZPORPHYR. (Germ.) f crystals only very frequent. 

(A) OLIGOCLASE-QTTARTZ-PORPHYRY. ^ The rock contains crystals of 
OLIGOKLAS-QUARZPORPHYR. (Germ.) \ oligoclase in addition to the 
orthoclase and the quartz. The oligoclase is distinguishable by 
its twin stripings, its different colour, or more advanced decom- 
position. Under this head we include, for instance, the brown 
porphyry of Manebach, in the Thuringian Forest, with its 
distinct orthoclase twin crystals of an inch long, containing, in 
addition to these, numerous smaller crystals of oligoclase, much 
decomposed. Frequently the oligoclase is transformed into a 
yellowish-green substance resembling steatite. Hermsdorf and 
Schonfeld in the Erzgebirge. 

Von Richthofen discovered certain porphyries at the Trost- 
burg and Monte Bocche, near Botzen in Tyrol, which, in addition 
to their quartz, only contain crystals of oligoclase, and (usually) 
some black mica, in a dark matrix. In the same neighbour- 
hood some porphyries contain quartz and orthoclase alone 
(at Bronzell and Pelegrin) ; others quartz, orthoclase, and some 
oligoclase (Castelruth, Blumau, Hoch-Eppen). Perhaps the 
beautiful brown porphyries of Lehnau near Kemnath, and of 
Kronberg near Erbendorf, are rocks containing oligoclase only. 
Their felspar crystals are all decomposed, although the matrix 
is unusually fresh. 

(i) SANIDINE-QUARTZ-PORPHYRY. ) Is a name given by Jenzsch to a 

SANIDIN-QUARZPORPHYR. (Germ.) } variety occurring at Zwickau in 

Saxony, containing sanidine and quartz. To the west of Oederan 



GRANITIC GROUP. 219 

near Freiberg, there occurs a porphyry containing crystals of 
orthoclase, sanidine, and quartz. 

It would be impossible to instance here all local differences, 
many of which only result from transmutation, or are to be re- 
garded but as accessory phenomena. Of this kind is the change of 
the felspar crystals into a greenish substance resembling steatite, 
occurring in a quartz-porphyry rock at theRaubschlb'sschen, near 
Weinheim. Again, in a porphyry of Manebach, near Ilmenau, 
rich in orthoclase, all the quartz crystals are encrusted with a 



greenish-blue coating, probably containing copper ; and in the 
gold-containing porphyry of Csetatye in Transylvania, the 
large diplohedrons of quartz are very much rounded oft) and the 



Quartz-porphyries are usually much rent by fissures, 
but sometimes are found of very regular columnar or 
of tabular-jointed structure. Tihey are probably never 
gnarled or irregularly spherical. They sometimes occupy 
connected regions of great extent, but in that case are by 
no means of uniform structure, consisting usually of many 
different varieties which penetrate and traverse each other 
in all directions, as in the Thuringian Forest, and near 
Botzen. They sometimes again form isolated dykes in 
granite, gneiss, &c., as near Freiberg. It is very rarely 
that they are found to have penetrated any more recent 
formations than the Devonian or Silurian. In Walden- 
burg in Silesia, however, they traverse the coal formations, 
and in the Thuringian Forest the Rothliegende, but these 
are exceptional cases. Their comportment in this respect 
is similar to that of granite, and with the difference of 
their containing throughout a somewhat higher proportion 
of silica, they would appear to represent but the porphy- 
ritic state of that rock, since they actually contain the 
elements of mica in small quantity. The compact state 
of their principal mass may to some extent be owing to 
their greater quantity of silica, but in all probability chiefly 
to their having originally cooled down more rapidly than 
granite, as is more especially likely to have been the case 
with the frequent isolated dykes and small masses of this 
rock. Quartz-porphyry as a rule, when found with granite, 
is more recent than the latter, bearing much the same 
relation to it as the trachyte-porphyries to the trachytes. 
Thus in Cornwall we find the quartz-porphyry or elvanite 
to have broken through the granite, and to form dykes or 
veins in that rock. 



220 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

References. 

G. Leonhard, Die quarzfiihrenden Porphyre, 1851. 

Naumann in the 5th No. of the Erlauter. zur geogn. Karte 
von Sachsen, 1845. 

Laspeyres on careful microscopic examination of the quartz- 
porphyries of Halle found the compact base to consist of 
felspar, quartz, and some mica. The crystals of felspar, ac- 
cording to him, had originally been sanidine, and are only 
in part transmuted to orthoclase. Zeitschr. d. deut. geol. 
Ges. vol. xvi. p. 867. 

Delesse, Porphyry from Lescines in Belgium, Bullet, de la Soc. 
Ge'ol. 1850 [21 vol. vii. p. 310. 

Jenzsch, on Sanidine-quartz-porphyry, Zeitschr. d. d. geol. Ges. 
1858, p. 49. 

v. Richthofen in the Zeitschr. d. d. geol. Ges. 1826, vol. viii. 
p. 644; v. L. u. Br. Jahrb. 1859, p. 312 ; and geogn. Beschr. 
von Siid-Tyrol, 1860, p. 112. 

Hochmuth, the Porphyries of Halle in the Bergwerksfreund, 
1847, vol. xi. p. 450. 

Streng in v. L. u. Br. Jahrb. 1860, pp. 129 and 257. 

H. Vogelsang on the Pyromerides of Corsica (Berggeist), 1862, 
NOB. 90 and 19 ; Jahrb. fur Mineralogie, 1863, p. 102. 

19. FELSTONE, FELSITE-ROCK AND FEL- 
SITE-SCHIST, PETKOSILEX,*EURITE, HAL- 
LEFLINTA. 

FELSTTFELS TJND FELSITSCHIEFER. (Germ.) 
A rock of compact texture, about the hardness of felspar, 
with dull or smooth conchoidal or fissile fracture ; 
colour yellowish, reddish, grey, greenish, or bluish, 
weathering white. 

Spec, grav 2-52-7 

Contains silica . . . . 7181 p. c. 

Gerhard was the first to discover that this rock, which 
we have already noticed as being identical with the ma- 
trix of the quartz-porphyries, consists chiefly of felspar, 
and he accordingly gave it the name of felsite. Some 
years later, Dolomieu surmised that it contained the 
essential ingredients of granite in a compact state, and 

* The name of petrosilex was first proposed by Brongniart, who 
applied it to felsite rocks, believing them to be identical with horn- 
stone. The name has stuck to these rocks in spite of the original 
error, and cannot well now be ignored. Some authors, wishing pro- 
bably to correct the original misconception, have, however, applied 
the name of petrosilex to hornstone, but this is simply to create un- 
necessary confusion better drop the name altogether. TKANSLATOE. 



GRANITIC GROUP. 221 

Daubisson proved it to consist of an intimate compound 
of felspar and quartz, and gave it the name eurite on ac- 
count of its fusibility. The same substance has also re- 
ceived the names of petrosilex, and in Scandinavia halle- 
jlinta, which are of earlier date than the names of felsite 
and felstone. All the later analyses of this rock have 
confirmed the fact that it contains both felspar and quartz, 
and besides these the elementary ingredients of some mica. 

In 1845, Durocher showed, by comparing the various 
analyses, that felstone, or petrosilex, is of the average 
chemical composition of granite, even quantitatively ; and 
it may therefore be regarded as a granite in compact 
state, something in the same way as basalt and aphanite 
respectively represent the compact states of the dolerites 
and the granular greenstones. Now, this fact is of im- 
portance with respect to the process of granite forma- 
tions, since we know that felsite rock, although it contains 
quartz, is as easily fusible as felspar alone. For we gather 
from it that the quartz of granite, when in combination 
with its other ingredients, might remain in a fluid state 
quite as long as the felspar and mica, so that the process 
of crystallisation of all might be contemporaneous, and it 
would then depend on the individual crystallizing force 
of each, which mineral would first develop its form. 
Quartz-porphyry, granitic-porphyry, and granite, with all 
their several varieties, are therefore products of essentially 
the same mineral dough, and probably they only differ by 
reason of slower or more rapid cooling or slight variations 
in the proportion of the several ingredients. That this 
igneous compound has most usually resulted in granite, 
especially in great connected regions of its development, 
probably proceeds from the fact of deep plutonic solidifi- 
cation ; or we may reverse the proposition and say, that 
wherever this igneous mass attained the solid state deep 
in the interior of the earth, granite, or a granitic rock, 
has been the result ; on the other hand, when it became 
solid at or nearer to the earth's surface, then trachyte 
(rhyolite) and trachy tic lavas were its products. 

Felstone may be divided into two principal varieties, 
the massive and the schistose. It goes over on the one 
hand very frequently into quartz-porphyry, or less usu- 
ally into granitic porphyry ; and on the other, it is con- 



222 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

nected by stages of transition with granulite and gneiss. 
The rock called Werner ite we reckon to the first of these 
two divisions : it has the character of an eruptive rock, 
whilst the foliated varieties of felsite are more closely 
connected with the metamorphic crystalline schists, and 
may be regarded as compact granulite or gneiss. 

Varieties. 

(a) FELSTOKE PROPER, orj Not fissile, usually of massive jointed 
PETROSILEX. I structure, or very much divided by 

PETROSILEX. (Germ.) f clefts and fissures. It is frequently 
PETROSILEX, Dolomieu. J found continuous with porphyry, but 

sometimes forming independent dykes 

in the same way as porphyry. Dippoldiswalde in Saxony, 
Bellmannsloos, near Tharand. 

(6) ' WERNERITE ROCK. \ Is the name given by Jasche to a 
WERXERITFELS. (Germ.) ( compact compound of common felspar 
SKAPOLIT-FELS. (Fr.) J and scapolite ( wern erite), with acces- 
sory admixtures of graphite, magnetic pyrites, and iron pyrites. 
It traverses the ironstone beds of Buchenberg at the Hartz. 
A similar rock, according to Axel Gadolin, occurs on tlie island 
of Pusu in the Ladoga Lake. 

(c) HALLEFLISTTA, or FELSITE-SCHIST. ] Foliated or unevenly lami- 
HALLEFLINTA, oder FELSITSCHIEFER. f nated. Sometimes contains 
HAiiEFKtNTA. (Fr.) j an admixture of chlorite in- 

* timately blended in its mass, 

and occasionally some mica. This rock is almost always found 
in parallel bedding with granulite or gneiss, into which it 
goes over by transition states. It is most frequently found in 
Sweden, and therefore, for the most part, should be con- 
sidered as belonging to the metamorphic schistous rocks, but it 
is not always possible distinctly to separate its different forms 
of development according to origin. 

The schistous as well as the massive varieties of felstone are 
very frequent among some of the older formations in the British 
Islands, making up whole mountain masses. 

It is most probable that the felsitic matrix of the quartz- 
containing porphyries of the granite group, is somewhat 
different in composition from that of the porphyrites which 
are free from quartz. The former will always contain 
more silica than that of the porphyrite, and its felsitic 
constituent will partake of the nature of orthoclase. This 
is our petrosilex. To outward appearance this difference 
is often scarcely appreciable, although the matrix of the 
porphyrites is usually (not always) darker in colour than 
that of the quartz-porphyries and granitic porphyries. 



GKAXITIC GROUP. 223 

References. 

Gerhard, Abhandl. d. k. Akad. d. Wissensch. zu Berlin, 1814 

and 1816, p. 12. 

Daubimson, Traite* de Ge*ognosie, 1st ed. 1819, vol. i. p. 112. 
Ditrocher, Compt. rend. 1845, vol. xx. p. 1277. 
Schweitzer, in Poggend. Ann. 1840, vol. li. p. 287. 
Kersten, in Poggend. Ann. 1843, vol. liii. p.^130. 
Wolff, Journ. f. prakt. Chemie, vol. xxxiv. p. 193, and vol. 

xxxvi. p. 412. 

Svanberp, Vet. Akad. Handl. 1850, p. 9. 
fftuiffhton, Journ. of the Geol. Soc. of Dublin, 1857, [7] p. 283; 

and Phil. Mag. 1857, [4] vol. xiv. p. 49. 

Jasche, on Wernerite rock, Mineralogische Studien, 1838, p. 4. 
A. Gadolin, on Wernerite rock, in the Verh. d. k. Kuss. mineral. 

Ges. at St. Petersburg, 1857-58, p. 85. 

20. PITCHSTONE and PITCHSTONE-POR- 
PHYRY. 

PECHSTEIN und PECHSTEINPORPHYR. (Germ.) 
REUNITE. (Fr.) 

The principal mass is homogeneous ; of vitreous pitch- 
like appearance; conchoidal fracture ; resinous lustre, 
translucent at the edges ; very variously coloured, viz., 
yelloiv, red, brown, black, and green; it sometimes 
encloses (porphyritically) small crystals of vitreous 
felspar, grains of quartz, and lamina of mica ; fre- 
quently also halls offelsite. 

Spec. grav. 2-22-3 

Contains silica 63 75 p. c. 

Pitchstone is evidently to be regarded only as a vitre- 
ous state of felsite rock, quartz-porphyry, or granite its 
chemical composition being essentially the same as that of 
these rocks, except that it contains more water than they, 
sometimes as much as 6 p. c. This may be one cause 
of its vitreous state. Its colour is dependent on the rela- 
tive proportions which it contains of the peroxide or the 
protoxide of iron and protoxide of manganese. The first 
of these gives the rock a red or yellow colour, the latter 
green, grey, and black. In spite of its large proportion 
of silica, thin splinters of pitchstone melt easily before 
the blowpipe to a white vesicular glass without intumes- 
cence. Formerly pitchstone was regarded as an inde- 
pendent mineral, but it is clearly nothing but a close 
compound of felspar and quartz, with which the elements 



224 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. 

of mica are also combined. Recently it has been even 
doubted whether this compound is really an amorphous 
vitreous mass, or only a very intimately blended crystal- 
line aggregate. It may be that this opinion has arisen 
from some few fine crystalline particles which swim in the 
prevailing vitreous mass. 

Crystals of sanidine are sometimes found porphyritically 
imbedded in the rock ; they are small, but usually quite 
fresh, and are frequently coated with a thin light-red 
crust, evidently caused by oxide of iron ; grains of quartz 
and laminae of mica are also found, but more rarely, and 
are often similarly coated. Instead of these crystals, or 
in addition to them, there also very frequently occur 
nodules or balls of felsite, very various in size and struc- 
ture. In the pitchstone-porphyry at Spechtshausen, near 
Tharand in Saxony, such are found varying from one-tenth 
of an inch to six inches diameter, consisting of compact 
felsite, and some of the very small balls of shining sani- 
dine. The larger ones occasionally contain veins of chal- 
cedony in their interior ; the grey pitchstone of Planitz, 
near Zwickau, contains balls of from one to five inches 
diameter veined inside in the manner of septaria, the 
veins narrowing towards the periphery and filled with 
chalcedony and quartz. At the Fichtenmiihle, near 
Meissen, a yellowish-brown pitchstone contains irregular 
nodules, whose size extends even to ten feet diameter, 
consisting of quartz-porphyry, with a matrix resembling 
hornstone. It would almost seem as if these were frag- 
ments torn from the adjoining quartz-porphyry (which is 
here traversed and disturbed by the pitchstone) and then 
rounded off in the convulsion. Near Corbitz, in the 
neighbourhood of Meissen, there is a pitchstone rock very 
much weathered, containing nodules from a quarter to 
three feet diameter ; these nodules consist of a compact 
felsitic mass, which itself contains other more compact and 
dark-coloured ball-shaped concretions of the same sub- 
stance. Similar phenomena with many modifications re- 
peatedly occur in the pitchstone of other localities. These 
nodules appear to answer to those in the pearlstone (sphe- 
rulites), which are smaller in size ; they are frequently 
coated with a deep-red crust or their surfaces much 
weathered. 



GRANITIC GROUP. 225 

The pitchstone of Planitz in Saxony is found to contain 
in some places small fragments of (so-called) mineral 
charcoal (a coal of woody texture without bitumen, and 
containing much silica) which indicate that the pitchstone 
has broken through the coal formation of that district. 

Scarcely any other minerals than those we have named 
are known to be similarly enclosed in pitchstone. 

This rock passes over into obsidian and pearlstone. 
By decomposition it becomes a kind of claystone rock, 
which variety Naumann called Pechthonstein (pitch-clay- 
stone). 

Varieties in Texture. 

(a) COMMON PITCHSTONE. \ Very variously coloured. Ex.g. 

I Trieb'isch Thai near Meissen. 



(6) PITCHSTONE-PORPHYRY. j With sanidine crystals. Mohorn 
PECHSTEINPORPHYR. (Germ.) I and Spechtshausen, between Frei- 

Kimxin POKPHYROlDE. (/>.) J ^ DreS den. 

A rock of this description is met with at Castelruth in 

Southern Tyrol ; it contains a felspar resembling sanidine and 

round grains of quartz, and v. Bichthofen describes it as a 

quartz-porphyry. 

(c) ARGILLACEOUS 'PITCHSTONE. \ The Pitch-claystone of Nau^ 

PECHTHONSTEIN, Naumann. (Germ.) I ma nn, a Stage of decompo- 

J sition not unfrequent near 
Meissen. 

Pitchstone is for the most part of irregular massive 
structure. It usually occurs associated with quartz-por- 
phyries, and traverses them in dykes ; probably, however, 
its geological age is not very different from that of the 
quartz-porphyries, and it would seem to bear somewhat 
the same relation to the porphyries as perlite and obsidian 
to the trachyte porphyries. 

The vitreous state of pitchstone is somewhat enigma- 
tical, inasmuch as that rock usually occurs with rocks of 
decidedly plutonic origin, and moreover contains a large 
proportion of water : Bischof and Jenzsch consider the 
glassy texture to be the consequence of transmutation by 
aqueous process, and only to be apparently vitreous. 
But it is very possible that under special circumstances in 
the interior of the earth, eruptive igneous masses may 
have cooled very rapidly, perhaps in consequence of the 
sudden accession of a large quantity of water, and so 
have become converted into a vitreous state containing 
water. 



226 ACIDIC IGNEOUS KOCKS. (2) PLUTONIC. 

References. 

Knox discovered a bituminous substance in pitchstone. 
Transact, of the Geol. Soc. 1811, vol. i. p. 278, and Ann. d. 
Phys..et Chem. 1823, vol. xxii.^ p. 44. 

Necker de Saussure. Voyages en Ecosse et aux lies Hebrides, 
vol. ii. p. 455. The pitchstone of the Hebrides exhibits 
under the lens a fine granular texture resembling basalt. 

Macculloch, Descr. of the Western Islands, vol. i. p. 520, on 
the pitchstone of the Hebrides. 

v. Oeynhausen and v. Decken, on the Pitchstone of the He- 
brides, in Karsten's Archiv. vol. i. p. 50. 

Haughton concludes from his analysis of pitchstone, that it con- 
sists of a combination of about 62 felspar, 30 stibite, and 
7 quartz. 

Naumann, on Pitchstone and Pitch-claystone from Meissen, in 
the Erlauter. zur. geogn. Karte v. Sachsen, 1844. No. 5, 
p. 184. 

Cotta, on the Pitchstone of Meissen and Tharand, Geognostiche 
Wanderungen, 1836, vol. i. pp. 40 and 104. 

Scheerer, Analysen u. Folgerungen in the Art. Pechstein in 
Liebig's Handworterbuch der Chemie, 1854, vol. vi. p. 105, 
and in v. L. u. Br. Jahrbuch, 1855, p. 60. 

Jenzsch considers pitchstone to be fine crystalline, and a pro- 
duct of transmutation and the balls of felsite in it, for re- 
mains of porphvry not yet transformed. Zeitsch. d. d. geol. 
Ges. 1856, p. 257. 

Rentzsch, Die Pechsteine, 1860. 

H. Fischer, on Pitchstone and Pearlstone, Zeitschr. der deutsch. 
geol. Ges. 1862, vol. xiv. p. 312. 



227 



CHAPTER II. 

METAMORPHIC CRYSTALLINE SCHISTS. 

THE term Metamorphic as applied to these rocks implies 
that they are the product of the metamorphosis of rocks 
originally sedimentary, and, although several gneiss rocks 
may have had another origin, they cannot be lithologically 
separated from those of undoubted metamorphic character. 

The designation of Crystalline Schist on the other hand 
rests solely on petrographical characteristics. 

The mineral composition of these rocks most resembles 
that of the plutonic division of the acidic igneous rocks, 
i.e. they consist (like those) chiefly of compounds of fel- 
spar, quartz, mica, talc, chlorite, and hornblende, and do 
not essentially contain pyroxene. We might indeed have 
anticipated the resemblance of the metamorphic rocks to 
the plutonic rather than the volcanic division of igneous 
rocks (whether basic or acidic) as their transmutation 
has probably taken place deep in the interior of the 
earth, therefore under plutonic influences ; and the fact 
that they contain more silica and less lime and magnesia 
on the average than the basic igneous rocks, is accounted 
for by the separate beds of carbonate of lime and magnesia 
(limestones and dolomites) which interlie the metamorphic 
rocks, whence we should expect to find the last mentioned 
rocks somewhat deficient in those bases. But we shall 
find that some of the crystalline schists are in fact rich in 
lime and magnesia, and therefore are more allied to the 
basic rocks. Those of prevailing acidic character are 
principally granulite, gneiss, mica-schist, quartz-schist, 
itacolumite and argillaceous mica-schist. The basic on the 
other hand are : chlorite-schist, talc-schist, and hornblende- 
schist, and others. 

All the rocks of this class are to be distinguished from 
the igneous by their foliated texture, and yet more by 
their alternate bedding in parallel layers or strata, and the 



228 CRYSTALLINE SCHISTS. 

traces which they often very distinctly show of internal 
stratification. These phenomena it is true are sometimes 
exceptionally met with in the igneous rocks, but in them 
they are the reverse of characteristic ; their foliated tex- 
ture, when it occurs, is usually to be explained by local 
pressure, their stratification by successive overflows of 
fused matter; as a general rule the igneous rocks also 
differ very widely in the character of their bedding from 
the metamorphic schists. Nevertheless there are actual 
petrographic transitions between the two, and in some in- 
dividual cases where the nature of the bedding is not very 
distinctly marked it is difficult to decide the character of a 
given rock. 

The properties which the crystalline schists have in 
common with the sedimentary rocks are stratification, 
fissile texture, and parallel alternating bedding ; on the 
other hand the schists are wanting in organic remains 
(fossils) and in mechanical aggregates. In their com- 
position they differ from the sedimentary rocks by the 
crystalline state of their mineral ingredients. There is, 
however, no very definite boundary between the two ; on 
the contrary there are series of distinct transitions from 
one to the other just as we might expect to find if the 
crystalline were really as we suppose them to be, the 
offspring of the sedimentary rocks. We moreover find 
that the greater part of the sedimentary rocks, and espe- 
cially the older ones, are no longer in their original state 
but are somewhat changed, doubtless by the identical 
influences which at last have transmuted them into crys- 
talline rocks and which are probably still in operation, 
viz. heat and pressure. 

The term Metamorphic, however, is in practice only 
applied to the extreme products of this slow process of 
transmutation, such as by assuming a crystalline state 
have entirely departed from that of their original deposit, 
although their connection with it may still be traced through 
stages of transition. This is simply a matter of usage, for 
looking to the meaning of the term., we might just as well 
call every clay-slate or firm sandstone metamorphic 
(transmuted) since they were not originally formed in the 
state in which we find them at the present day. 

Por these and other reasons it is difficult to prescribe 



FELSPAR GROUP. 229 

a definite and consistent limit to metamorphic rocks. 
From a geological point of view we ought to include 
in that term most granular limestone, serpentine, gra- 
phite, magnetic iron-ore, &c., and reject many kinds of 
gneiss and granulite as being irruptive ; but in a system 
of lithology this treatment, however logically correct, 
would lead to so many inconveniences and difficulties as to 
render it impossible in practice. 

For these reasons we have not made use of the general 
designation Metamorphic rocks as the title for this 
chapter, but chosen the more restricted term of Metamor- 
phic crystalline schists. These for the most part are 
compounds rich in silica, which, in their chemical com- 
lHition approach Bunsen's formula for the normal 
trachytic rocks. Some few, however, are poor in silica 
and resemble the basic igneous rocks in composition. 
We do not propose to divide the metamorphic schists into 
basic and acidic groups ; we prefer to group them accord- 
ing to their leading mineral ingredients without attempting 
a strict scientific arrangement, except that we begin with 
those which in their mineral character bear the greatest 
resemblance to the granite rocks and place those last 
which approach most in character to the unchanged 
sedimentary rocks. 

CRYSTALLINE SCHISTS, RICH IN FELSPAR. 
(Granulite and Gneiss.) 

21. GRANULITE, LEPTYNITE. 

GRANULTT, WEISSSTEIN. (Germ.) 
LEPTYNITE, Haiiy. (Fr.) 

A fine-grained to compact fissile compound of felspar and 
quartz ) usually with some mica. 

Spec. grav. . ... . 2-62-7 

Contains silica . . 70 80 p. c. 

This rock, oil account of its frequent white or light- 
yellowish colour, was formerly called weissstein (white 
stone) ; but as the same mineral compound also occurs of 
a dark colour, Weiss proposed to substitute the name of 
granulite, which has now been generally adopted. Its 
mineral composition is for the most part that of a granite 
or gneiss (a red gneiss), with very little mica. Its cha- 



230 CRYSTALLINE SCHISTS. 

racteristic varieties are nevertheless easily to be distin- 
guished from granite and gneiss, as will appear from a 
more special description of the rock. Intermediate grades 
of uncertain character and transitions are, however, 
frequent, and if these occur in the midst of gneiss or 
granite, we reckon them without hesitation, to those rocks, 
and call them granulitic gneiss, or granulitic granite ; but 
if found in granulitic regions the same rocks would be 
properly termed gneissic granulite, and reckoned to the 
granulites. 

The felspar of granulite is mostly orthoclase ; some- 
times, however, in part oligoclase. It is intimately 
blended with the quartz, which is Jess in quantity, 
or at all events is less apparent, than in granite or 
gneiss. The free quartz forms few and very thin sepa- 
rate layers, or flat lenticular grains, which are to be most 
distinctly seen when the rock is weathered. The mica 
appears in small scattered laminae, disposed in parallel 
planes, or if sometimes found connected, scaly seams en- 
tirely dividing the rock, which otherwise is an intimate 
compound of felspar and quartz. In both cases the mica 
increases the fissile texture of the rock. It is usually a 
white variety of mica seldom black. The felspar, which 
is always predominant, is usually white, yellowish, or 
light-red ; and these are, therefore, the prevailing colours 
of the rock. The quartz is never dark-coloured, seldom 
transparent, and usually white. In a section of the rock 
the seams of mica sometimes produce riband stripings of 
dark colour. There are, however, varieties of granulite 
in which the whole mass is of a blackish-green to almost 
quite black colour (owing perhaps to protoxide of iron); 
for these the old name of weissstein is inappropriate. 

We repeat, then, that the essential constituents of the 
rock are its felspar and quartz, and a small proportion of 
mica. In addition to these, red garnets often appear 
disseminated through the mass in small grains or crystals ; 
where little or no mica is present, then these garnets are 
especially frequent, and this is the most characteristic 
composition of granulite. Where much mica is' found, the 
garnets appear to fail, and varieties of this latter kind 
form the transitions into gneiss. Another characteristic 
accessory ingredient of granulite, though but * sparingly 



FELSPAR GROUP. 231 

distributed, is blue disthene (kyanite). Schorl and horn- 
blende also occur, but more locally. 

This rock forms transitions into granite by assuming a 
more distinctly granular, and less fissile texture, into 
gneiss, by the increase of its mica, and into felsite-schist, 
when its mica disappears and the mass becomes quite 
compact. 

Varieties in Texture. 

(d) COMMON GRANULITE. ) White, yellowish, or flesh-red, 

GEMEINER GRANULIT. (Germ.) I with little or no mica, contains 
LEPTYNITK COMMUN. (Fr.) J ^^ g^et^ ^d frequently 

some disthene. It is more laminated than properly speaking 
foliated or slaty. Rosswein in Saxony. 

(b) RIBAND-STRIPED GRANTJLITE. ) Striped by parallel seams of 

BAXDSTREIFIGER GRANULIT. (Germ.) L mica, interlying the main 

J mass of felspar and quartz. 

On the Zschopau between Sachsenburg and Schonborn in 
Saxony. 

(c) MICACEOUS GRANULITE or GNEISS-GRANULITE. ) With few or no 

GLIMMERRHICHER oder GNEISSGRANUUT. (Germ.) I garnets. Mitt- 
LKPTYNITE MICACE. (Fr.) J we id a in Saxony. 

(d) GRANITIC GRANULITE. ] More granular than fissile. This 

GRANrrGRANULrr. (Germ.) I variety passes into a kind of granite 
LEFTYNITE GRENU. (Fr.) j w hich contains little mica, and where 
it occurs in the form of dykes or veins, it may be considered 
as a granite. Neighbourhood of Herrnhut in Saxony. 



. protoxide 

LEPTYNITE NOIR. (Fr.) I of iron. Tenig in Saxony. 

(/) SPOTTED GRANULITE. ) "With dark spots caused by horn- 
GEFLECKTER oder FORELLKN- f blende. Glocknitzer Schlossberg, 

ORAKUZ^T. (Germ.) ) Wiener Neustadt. 

(0) SCHORLACEOUS GRANULITE. ] With considerable quantity 
TOURMALINGRANULIT. (Germ.) [ o f 8C horl in its composition. 



) W 
of 
*) Ac 



LEPTYNITE TOURMAJJMFERE. (Fr.) T TT 

') According to v. Hochstetter, 

it occurs near Krummau in Bohemia, 

Granulite is usually of very regular tabular-jointed 
structure, disposed parallel to the foliation or lamination 
of the rock ; but besides this more or less horizontal 
jointing, it is also usually intersected at right angles by 
cross joints, somewhat crooked, but whose surfaces are 
smooth. This latter jointing is characteristic of granulite, 
which by its means may sometimes be distinguished from 
gneiss at a considerable distance. 

In Saxony, Bohemia, and Moravia, this rock fills con- 
siderable regions of elliptical shape, surrounded by other 



232 CRYSTALLINE SCHISTS. 

crystalline schists. The granulite region of Mittweida 
in Saxony is surrounded and overlayed with mica-schist 
and dichroite-gneiss, of which latter it contains large frag- 
ments. It is also penetrated in all directions by numerous 
often very distinct, but narrow dykes or veins of granite. 
JSTaumann considers this region to be of eruptive origin. 
Metamorphic rocks may possibly in some cases have 
become eruptive here. 

References. 

JEnyelbrecht, Kurze Beschreibung des Weisssteins, 1802. 
Weiss, Neue Schriften naturf. Freunde in Berlin, vol. iv. 

p. 350. 
fforniff, Analysen des Kremser Granulits, in den Sitzimgs- 

berichten der k. k. Akademie zu Wien, 1851, vol. vii. p. 586. 
v. Hochstetter, Granulit von Krummau, in Jahrb. d. geol. 

Reichsanst. 1854, vol. v. p. 11, and the Corresp.-Bl. d. geol. 

mineral. Ver. zu Eegensburg, 1853, p. 157. 
Naumann, in Erlauter. z. geogn. Karte v. Sachsen, No. 1, 

p. 9, and 1838, No. 2, p. 19 ; Karsten's Archiv, 1832, vol. v. 

p. 393, and Jahrb. d. geol. Reichsanst. 1856, p. 766. 
Zirkel, Granulit-analysen, in Poggendorff's Annalen, vol. cxxii. 

p. 624. 

22. GNEISS. 

GNEISS, GNEUSS. (Germ.} 
GNEISS. (Fr.) 

A crystalline-granular compound of quartz, felspar, and 
mica; texture foliated. 

Spec. grav. . . . * . 2-6 27 
Contains silica 64 76 p. c. 

The mineral composition of gneiss is precisely the same 
as that of granite ; the only petrographic difference be- 
tween the two rocks consists in the foliated texture of the 
former. We may, therefore, say that gneiss is the name 
given to schistose granite. The term gneiss originated 
with the Freiberg miners, who from ancient times have 
used it to designate the rock in which their veins of silver 
ore were found, and more especially such parts of the 
rock as were much decomposed. 

The felspar of gneiss is usually orthoclase, sometimes 
with oligoclase, and perhaps even albite. The orthoclase 
is white, grey, yellow, or reddish, and on fresh cleavage 
surfaces has mother-of-pearl lustre. Usually it occurs 



FELSPAR GROUP. 233 

only in small grains, sometimes larger crystals or lentil- 
shaped masses so called, swellings or eyes (Schwielen, 
Augen), with the regular twin growth peculiar to ortho- 
clase (porphyritic gneiss, augen-gneiss). The oligoclase 
which occurs with and subordinate to the orthoclase or 
(more rarely) as its substitute may usually be recognised 
by its twin stripings, more resinous lustre, or more 
advanced decomposition. 

The quartz forms small white or grey lentil-shaped 
grains or irregular excrescences upon the felspar ; more- 
over it often appears in separate larger and irregular 
masses. 

The mica is usually potash-mica (more rarely magnesia- 
mica), brown, black, white, or dark-green ; and some- 
times in the same gneiss different coloured micas occur 
together. 

Gneiss occasionally contains accessory ingredients of 
various kinds, such as chlorite, talc, graphite, micaceous 
iron, dichroite, garnet, tourmaline, andalusite, pistacite, 
zircon, disthene, rutile, titanite, pyrites, magnetic iron- 
ore, &c. 

Sometimes one or other of these minerals is abundant, 
and assume the character of an essential ingredient ; thus, 
for instance, the prevalence of hornblende occasions a tran- 
sition from ordinary gneiss into syenite-gneiss, the presence 
of chlorite or talc into protogine-gneiss, &c. These 
different varieties in composition are easy of recognition. 

It is more difficult in many cases to recognise the 
perhaps more important difference between the so-called 
' red ' and * grey ' gneiss. It was formerly considered 
that all gneiss was of metamorphic origin, but it has of 
late years been established beyond a doubt that many 
kinds of gneiss are irruptive, and some geologists have 
gone so far as to regard all gneiss as of igneous origin. 

In the mining districts of the Erzgebirge it had been 
observed that the veins in the red varieties of gneiss were 
usually non-metalliferous, although within a short distance 
the same veins traversing grey gneiss were rich in ore. 

Previously to the year 1844, we ourselves had observed 
red gneiss of a distinctly eruptive character, forming veins 
in the grey gneiss, which latter is the prevalent rock of 
the mining districts of the Erzgebirge ; the result of 



234 CRYSTALLINE SCHISTS. 

these observations we published in von Leonhard's 
Almanack. (Vide v. L. u. Br. Jahrb. 1844, p. 681.) 

Subsequently Professor Scheerer received a commission 
from the Saxon mining authorities, to analyse several 
kinds of gneiss, with a view to discover the cause of the 
superior richness of the metalliferous veins in the grey 
gneiss ; and he found amongst other chemical differences 
that the red gneiss usually, if not always, contained a 
considerably larger proportion of silica than the grey. 

Accordingly the gneiss of the Erzgebirge came to be 
divided into two principal classes of distinct mineralogical 
as well as chemical characters, termed respectively red 
gneiss and grey gneiss. 

The red gneiss is not, however, always to be easily dis- 
tinguished from the grey gneiss, as the colours of the two 
distinct classes do not in every case correspond with the 
names that have been given to them, and some so-called 
grey gneiss is of red colour, and vice versa ; and although 
in several instances the bedding of the red gneiss shows 
it to be of distinctly irruptive character, yet the bedding 
of both kinds of gneiss is frequently indistinct and un- 
certain, or might be capable of various interpretations, 
and therefore would not alone serve the purposes of litho- 
logical distinction. The recognised and only reliable 
distinction consists in the proportion of silica, only to be 
arrived at by chemical analysis of the rock. These con- 
siderations compel us, regardless of origin, to retain the 
usual classification for all gneissic rocks, and notwith- 
standing the irruptive character of some varieties, to treat 
them collectively in this place amongst the metamorphic 
rocks. 

We proceed to define these two principal classes of 
gneiss, and (to avoid attaching an undue importance to 
their mere colour) we propose the name of gneissite for 
the variety formerly known as the red gneiss : 

A. GNEISSITE, or RED GNEISS. (Rother Gneiss oder 
Gneissit. Germ.) The felspar of the compound appears 
to be always orthoclase, and to be the predominant in- 
gredient. The mica is always white, or at all events not 
dark-coloured, not abundant in quantity, but usually 
scattered through the mass in thin straight laminae. 

The rock contains 74 76 per cent, of silica. 



FELSPAR GROUP. 235 

According to Scheerer,it is an acidic compound, a sesqui- 
silicate. Its extreme varieties are easily to be recognised, 
and may be better distinguished from the grey gneiss than 
gneiss from many varieties of granulite. Its felspar is 
usually reddish, exceptionally, however, white or greyish. 

In the Erzgebirge this gneissite is found in irregular 
tracts, and sometimes forming distinct dykes or veins in 
the ordinary gneiss, of which it frequently encloses frag- 
ments. We may therefore say that there it comports 
itself as an eruptive igneous rock towards the common 
gneiss, and geologically speaking should perhaps properly 
be considered a granite. But as its bedding is frequently 
indistinct and the character of single specimens is often 
not to be recognised with certainty, and as some kinds of 
gneissite may very possibly be of metamorphic origin, we 
cannot usefully separate it lithologically from every other 
gneiss by taking it out of the class of the crystalline schists. 

B. GREY GNEISS. (Grauer Gneiss. Germ.) The 
felspar of the compound is principally orthoclase, some- 
times, however, with the orthoclase some oligoclase or 
albite is associated. The mica is partly dark-coloured 
(ferruginous and more basic than that of the gneissite), 
it is moreover abundant, whence the rock usually assumes 
a dark or grey colour. 

The rock contains 64 67 per cent, of silica. 

According to Scheerer, it is a neutral silicate. The 
normal Freiberg variety is granular, scaly, and unevenly 
foliated. The felspar is usually white or grey, but some- 
times of a reddish colour. The mica is mostly dark- 
coloured, but some white. Mica occasionally occurs in 
the compound. Accordingly, the differences between 
these two normal varieties (the gneissite and the grey 
gneiss) may be stated as follows : 



Gneissite, or Red Gneiss. 

Content of silica, 74 76 p. c. 
Felspar orthoclase only. 

Mica in small quantity and 
li<rht-coloured. 

Approximate proportion of mineral 
ingredients. 
30 quartz 
60 felspar 

10 illicit 



Ordinary, or Grey Gneiss. 

Content of silica, 64 67 p. c. 
Felspar orthoclase and sometimes 

oligoclase. 
Mica abundant and dark-coloured. 

Approximate proportion of mineral 
ingredients. 
25 quartz 
45 felspar 
30 mica 



236 CKYSTALLINE SCHISTS. 

The mica (both of the gneissite and grey gneiss) usu- 
ally contains about 4 per cent, water, and this water 
Scheerer regards as an original ingredient of the mineral 
entering into its chemical composition, as a base to the 
silicic acid. 

Besides these two extreme kinds of gneiss, it appears 
that many intermediate grades exist, which may be col- 
lectively designated as 

C. MEDIUM GNEISS. (Mittelgneiss, Germ.) Gneiss 
containing an intermediate proportion of silica between 
that of the gneissite and the grey gneiss. The mineral 
character sometimes resembles the one and sometimes the 
other of those two extremes. 

Scheerer has endeavoured to show that, chemically 
speaking, this medium gneiss C forms an independent 
rock or variety, whose proportion of silica is constant be- 
tween 69 and 70 percent., and that it therefore uniformly 
and essentially differs from the varieties A and B. (Vide 
Scheerer iiber die Gneusse des Erzgebirges in the Zeit- 
schrift der deutschen geol. Ges. vol. xiv. ; also published 
separately, Berlin, 1862.) 

Later analyses have, however, shown the existence of 
gneisses varying in their composition, and especially in 
the proportion of silica which they contain, as much from 
the normal medium gneiss as from the two extreme va- 
rieties of red and grey gneiss. Therefore we must guard 
ourselves against expecting any sharply defined chemical 
character in the different varieties which come under our 
notice. 

We must remember that it is only of late years that 
attention has been called to this subject, and with the 
utmost chemical industry but few analyses, comparatively 
speaking, have yet been made with the special object of 
distinguishing different species of gneiss. These analyses 
have chiefly been conducted at Freiberg, and mainly with 
a view to ascertain and discover whether any and what 
differences of rock coincide with the richness of metal- 
liferous veins in the Erzgebirge. It appears to be an 
established fact that the grey gneiss is more favourable 
for the yield of rich veins than the gneissite or red 
gneiss. 

This is a very interesting fact, which deserves the 



FELSPAR GROUP. 237 

attention of geologists. At present we are not aware of 
any thoroughly satisfactory explanation of it, unless we 
adopt Scheerer's theory that the iron of the mica in the 
grey gneiss is the cause of its advantage in this important 
respect. He has shewn that the mica is invariably decom- 
posed for some distance on each side of the metalliferous 
veins. 

The gneiss of the Erzgebirge is undoubtedly partly 
irrnptive and partly metamorphic ; and we believe that 
its character in this respect must always be determined 
rather from observation of the bedding than from the 
chemical composition of each individual rock ; at all 
events, the analyses which have hitherto been made do 
not justify the conclusion that rocks of a definite propor- 
tion of silica are confined to any particular geological 
origin, or vice versa that rocks of the same geological 
origin are uniformly of one chemical character. 

It would, indeed, be somewhat remarkable if it were 
found that the collective elementary ingredients of a rock 
like gneiss, consisting of three separate minerals, were 
combined in such uniform proportions as to be capable 
of being expressed by a simple chemical formula ; we 
should rather expect that from a mass so constituted a 
homogeneous rather than a compound rock would have 
resulted. We are, however, ready to admit that the 
strangeness of a phenomenon to our preconceived ideas is 
no valid argument against its truth. 

In the present state of our chemical investigations, 
therefore, we can only seek approximately to range all 
known gneisses under one or other of the three heads we 
have named. If geologists in different parts of the world 
will assist in this work, there is room for hope that some 
general law may be discovered which shall advance the 
state of science with respect both to the origin of gneiss 
and the causes which have influenced the superior rich- 
ness of the metalliferous veins in some rocks to the 
exclusion of others. 

Independently of the division into gneissite, grey gneiss 
and medium gneiss, which, however important geologi- 
cally, depends mainly on chemical, and only partly on 
mineralogical, differences, we have the following varieties 
in texture and composition. 



238 CRYSTALLINE SCHISTS. 

Varieties in Texture. 

(a) COMMON FREIBERG GNEISS. ] Belongs to the class of grey 
FREIBERGER NORMALGNEISS. (Germ.) L o-neiss. The flakes or laminae 
GNEISS COMMON ou NORMAL. (Fr.) J g f mica are digtributed in 

parallel planes through the granular compound of felspar and 
quartz. The rock has often a folded or wavy texture. In the 
immediate neighbourhood of metalliferous veins, near Freiberg, 
it is impregnated with pyrites, sometimes with arsenical pyrites, 
galena or blende, by which latter its decomposition is much 
accelerated. 

(J) PORPHTRITIC GNEISS. ] In the otherwise uniform schis- 

AUGEXGNEISS oder PORPHYR- j. tose mass there occur at in- 

S?SSffiy^!) > tervals large egg-shaped crystals 

of orthoclase (usually they are 

twin crystals, sometimes they are amorphous), round which 
the foliated texture bends itself with a wavy sweep. This is 
very characteristically developed near Schwartzenberg in the 
Erzgebirge, Kedwitz in the Fichtelgebirge. 

(c) STANGEL GNEISS, COARSELY FIBROUS GNEISS. I The ingredients 

STANGELGNEISS oder HOLZGNEISS. (Germ.) > are disposed in 

a fibrous manner towards one direction, so that a peculiar 
linear parallel conformation is produced. The stalks or fibres 
may consist of felspar and quartz, or of stripes of mica. In 
the extreme development of this texture a wood-like confor- 
mation is produced, which almost supersedes the schistose 
texture. Lippersdorf, Lengefeld, Weissenborn, and Weig- 
mannsdorf, near Freiberg, Saxony, Sonnenberg in Bohemia. 

(d) VERY FINE SLATY GNEISS | All the mineral parts small 5 the 

or SLATE-GNEISS. j- numerous parallel flakes of mica 
SCHIEPERGNEISS. (Germ.) j occasion very distinct slaty texture. 
In the cleavage, mica alone is usually seen. 

(e) VERY FINE-GRAINED, ALMOST ) With only indistinct foliated tex- 

COMPACT GNEISS. Y ture. Radegrube, near Freiberg, 

GNEISS A GRAINS FINS. (Fr.) J Radeberg, near Dresden. 

(/) LAGEN GNEISS. j Quartz and felspar on the one hand, and 

LAGENGNEISS. (Germ.) L the mica on the other, form thin parallel 

GNEISS RUBANE. (Fr.)] ^ mutuaJ Q y altera ating seams or layers, 

which, in the cross section, occasion a ribbon striping. 

(g) GRANITE-GNEISS or GRANITIC GNEISS. \ With very 

GRANTTGNEISS oder GRAXITAHNLICHER GNEISS. (Germ.) } granular and 

only indistinctly foliated texture, forming a transition state 

between gneiss and granite. Sageritz near Grossenhain, Boxdorf 

near Moritzburg, Brambach in the Voigtland, Hofles near Eiger. 

Naumann has collected into one class, under the name of 

' CORNUBIATES,' several exceptional varieties of gneiss, some 

compact, or of very indistinctly compound texture, others of 

contorted foliated texture. They occur variously, usually as 

contact formations at the margins of more recent igneous rocks. 

Saussure called them ' PALAIOPETRE,' Boase ' PROTEOLITE.' 

Properly speaking they belong only geologically, and not pe- 

trographically to gneiss, and they can only be classed as gneiss 

where their position and bedding give them that character. 



FELSPAE GROUP. 239 

Varieties in Composition. 

(ft) GRANULITE-GNEISS. \ With very little mica, and that usually 
GKAxcuKiNKiss. (Germ.)) white. Felspar predominates, and is 
often intimately combined with quartz. Always belongs to 
the gneissite or red gneiss. Grosswaltersdorf near Freiberg, 
Lauterbach near Marienberg, Mautern near Molk, Poppenreut 
near Miinchberg. Hochberg near Eger; and a variety with 
dark-coloured mica, Fahrnleiten, near the Schneeberg, in the 
Fichtelgebirge. 

(0 MICACEOUS GNEISS. | Forming a transition state into mica- 
GLIMMEROXEISS. (Germ.) } schist, with much mica, chiefly dark- 
coloured, and little felspar ; usually of a line foliated texture. 
Near Kabenau and Dippoldiswalde in Saxony, where it occurs 
between strata of ordinary gneiss ; also, in like manner, at 
Gastein in the Alps. 

(k) GM;ISS VKUV RICH IN QUARTZ, and going over into a kind of 
quartz-schist. 

(/) SYENITIC GNEISS. ] With characteristic admixture of horn- 

SYENITGNEISS. (Germ.) I blende. Neighbourhood of Aschaffen- 



Fichtelgebirge. 

(m) PROTOGINE-GNEISS. ] With chlorite or talc instead of mica. 
PROTOGINGNEISS. (Germ.) ^Oberhasli and Mont Blanc in the Alps. 
Fr.) )M tle Q oldber near 



Fichtelgebirge, a somewhat indistinct protogine-gneiss encloses 

fragments of clay-slate, and from this would appear to be of 

igneous (irruptive) character. 

(n) ADULARIA-GNEISS. \ With adularia in the place of the usual 
ADULARONEISS. (Germ.) \ orthoclase. Very widely spread in the 

Alps, e.g. St. Gotthard. 

(o) OLIGOCLASE-GNEISS. ^ With oligoclase in the place of ortho- 
OLIGOKLASGNEISS. (Germ.) \ c lase. According to v. Hochstetter, the 

lofty Adam's Peak of Ceylon (7,000ft.) consists of this rock. 

It contains many garnets, and is found in alternate layers with 

syenite-gneiss, granulite-gneiss, granulite, and hornblende-slate. 
(p) GNEISS WITH TWO KINDS OF MICA, white and black, occurs very 

frequently. Seerenbach near Tharand, Lauenstein in the Erz- 

gebirge, Steingriin near Eger. 
(q) DICHROITE-GNEISS. | With dichroite in the place of mica. 



DICHROITGNEISS. (Germ.) Found in the margin of the Saxon 

0*1088 AVEC DlCHKOrTK g 



selburg. 

(r) MICACEOUS IRON GNEISS. | With micaceous iron instead of com- 
i-:.>KxLiMiaROKEi.7rm.) } mon m i ca . i n the southern Fichtel- 

gebirge. 
(a) GRAPHITE-GNEISS. \ With graphite in the place of the mica. 

&BU*puBM.(0*m);Neax Passau, on the Danube. 
(<) ALPIXITE. | Is a name given by Simler to a schistose com- 

ALP (6?i Simler ' [pound of quartz, 'felspar (oligoclase), and a 
j flaky green mineral, probably belonging to the 
mica species, but certainlv not chlorite or talc (liber die Petro- 
geneses. Berne, 1862). Very frequent in the Alps. 



240 CRYSTALLINE SCHISTS. 

The above are the principal varieties of this very im- 
portant rock ; it would neither be possible nor desirable 
to enumerate every modification of differing texture and 
composition. 

Gneiss, in addition to those of its accessory ingredients 
which have been already mentioned, sometimes contains 
irregular concretions or minute veins of quartz, felspar, or 
a kind of granite resembling the graphic granite. 

The foliated texture of gneiss is a universal charac- 
teristic. Gneiss is also usually stratified or jointed in a 
direction parallel to its texture. At all events a divergence 
from this direction has not been hitherto observed. Be- 
sides this tabular jointing there is sometimes a tolerably 
regular oblique parallelopipedic jointing dividing the rock 
into irregular rhombs, two of whose faces correspond with 
the stratification of the rock. 

Gneiss is found in extensive regions in many mountain 
districts. The mountains which it forms are of very 
various shapes, according to the position and direction of 
the foliated texture. If this be horizontal then we have 
fiat undulating table-lands where valleys appear like cuts 
in the otherwise uniform surface. If, however, the bed- 
ding of the rock has been upheaved so that the parallel 
planes of the texture assume a vertical position, then it 
forms jagged alpine heights. Both the bedding and the 
texture are frequently very much contorted. 

Gneiss, wherever we can approximately determine its 
geological age, is found to be of high antiquity. It occurs 
with granite rocks usually lying above them, but often 
penetrated and traversed by them. The oldest sedi- 
mentary rocks usually overlie the gneiss, but there are 
some exceptions where, as in the Alps and the Fichtelge- 
birge, the gneiss is found uppermost ; these exceptions 
are capable of being explained by disturbances of the 
original bedding. 

References. 

Scheerer, Chemische Untersuclmiigen des Gneisses im Jahrb. d. 
k. sachs. Bergakademie z. Freiberg, 1858, p. 210, 1861, 
p. 252, 1862, p. 188 ; Berg- u. Hiittenm. Zeitung, 1861, 
p. 188 ; and v. L. u. Br. Jahrb. 1861, p. 613 ; Zeitsch. d. d. 
geol. Gesells. 1862; also separately published under the 
title of ' Die Gneusse des Erzgebirges.' 



QUARTZ GROUP. 241 

Naumann, Erlauter. z. geogn. Karte v. Sachsen, No. 2, p. 265, 

and No. 5, p. 51. 
Cotta, Rother u. Grauer Gneiss, in v. L. u. Br. Jahrb. 1844, 

p. 681, and 1854, p. 39. 

Credner, Syenitgneiss, in v. L. u. Br. Jahrb. 1850, p. 549. 
Peters, Syenitgneiss, in Jahrb. d. geol. Reichsanst. 1853, p. 236. 
Kittel, Syenitgneiss, Umgegend v. Aschaffenburg, 1840, pp. 

11 and 27. 
v. Rath, Gneiss in Graubiindten, Zeitschr. d. d. geol. Ges. 1858, 

p. 199. 
Fournet, Gneiss der Alpen, Me*m. sur la Ge*ol. de la part des 

Alpes, p. 29. 

Boose, Transact, of the Geol. Soc. of Cornwall, vol. vi. p. 390. 
Quincke, Schonfeld and Roscoe, Analysen in Ann. der Chem. 

u. Pharm. 1854, vol.xci. p. 306, and 1856, vol. xcix. p. 239 ; 

v. L. u. Br. Jahrb. 1855, p. 453. 
v. Hochstetter, Oligoklasgneiss, Novarra-Reise, 1861, Th. i. 

p. 324 

CRYSTALLINE SCHISTS RICH IN QUARTZ. 
(Mica-schist, Quartz-schist, Itacolumite.) 

23. MICA-SCHIST. 

GLIMMERSCHIEFER. (Germ.) 
MICASCHISTE, Brvngniart. (Fr.) 

A crystalline schistose compound of mica and quartz. 

Spec. grav. . . . V ; . 27 3-1 
Contains silica . .. > . . ' 6982 p. c. 

Its texture is always foliated, but with many varieties of 
modification. Its composition varies between two ex- 
tremes ; one consisting almost entirely of mica, the other 
(quartz-schist) almost entirely of quartz. 

The mica is most usually the optically biaxial potash- 
mica, but sometimes dark magnesia-mica, damourite, or 
paragonite. Two different kinds of mica occasionally occur 
together in the same rock. Usually the laminae, whether 
large or small, all lie in planes approximately parallel to 
each other, and thereby occasion the foliated texture of 
the rock ; it is rare to find them in diverging directions. 

The mode in w^ich the mica and quartz are united is 
somewhat various. In those varieties which contain the 
most mica the small grains or lenticular particles of quartz 
usually lie hidden in it, and the rock appears almost 
exclusively to consist of mica. If the quantity of quartz 
be greater, then its larger lenticular masses are dis- 
tinctly prominent amongst the mica in a cross fracture of 

to 



242 . CRYSTALLINE SCHISTS. 

the rock. Again, these lenticular bodies extend and 
are elongated into thin parallel layers of granular com- 
position, and sometimes themselves enclose small flakes of 
mica of divergent direction. Those varieties which are 
very rich in quartz consist almost entirely of that mineral, 
and only receive a foliated texture from the thin parallel 
layers of mica imbedded in the quartz. 

Sometimes (and even in varieties very rich in mica) in 
addition to the quartz contained in the main mass of the 
rock, irregularly swollen-shaped masses and veins of quartz 
occur, round which the foliated texture bends itself, or 
there are found actual seams of quartz in the rock. 
Garnets frequently occur in such abundance as to be 
characteristic for certain varieties. They are red or 
brown, and occur porphyritically as isolated crystals, un- 
usually rhombic dodecahedrons, from the size of a scarcely 
visible grain to that of an apple. In each individual rock, 
however, these are usually nearly of a uniform size. 
The flakes of mica bend round these crystals as if they 
had been pushed on one side during the process of their 
formation. Near Fahlun, in Sweden, there is a magnesian 
variety of mica-schist containing very large dodecahedrons 
of garnet, which are sometimes split into two parts which 
have become joined together again in a displaced position. 

Mica-schist also frequently contains some or other of 
the following as accessory ingredients : schorl, staurolite, 
disthene,andalusite, hornblende, chiastolite, beryl, chlorite, 
talc, and felspar less frequently, also graphite, micaceous 
iron, cordierite, pyrites, or cinnabar, &c. 

Some of these accessory ingredients are characteristic 
for certain varieties of mica-schist, and they also occasion 
transitions from mica-schist into other rocks. Thus the 
presence of chlorite occasions a transition into chlorite- 
schist,of talc into talc-schist, of felspar into gneiss, of schorl 
into schorl-schist, of graphite into graphite-schist, of mi- 
caceous iron into ferruginous mica-schist. If the mass 
becomes compact, and especially if the mica should be- 
come indistinctly blended with the other ingredients, then 
the rock passes over into argillaceous mica-schist, and finally 
into clay-slate, so that we have thus a complete series of 
transitions from the most distinct gneiss through mica- 
schist into clay-slate. But we know of no transition from 



QUARTZ GROUP. 243 

mica-schist into the granular greisen, although the com- 
position of those two rocks is mineralogically the same. 

Varieties in Texture. 

(a) COMMON MICA-SCHIST. \ Somewhat unevenly fo- 

GEMEINEH GLIMMBBSCHIEFER. (SCHTTPPEN- f liated, of a scaly ap- 

GLIMMKKM-HIKFEU.) (Germ.) .,1 V r , 

MICASCHISI-E COMMUN ou NORMAL, (Fr.) J pearauce with very much 
mica, but the quartz nevertheless distinct. Of very frequent 
occurrence. 
(6) MICA-SCHIST, VERY FINE AND] 

EVEN IN TEXTURE. Y Also frequent. 

PLANGLIMMERSCHIEFER. (Germ.) ) 

(c) MICA-SCHIST OF WAVY TEXTURE. ) A delicate wave-like tex- 

FAI/TENGLIMMERSCHIEFER. (Germ.) L ture. occasions a very dis- 

J tine? linear parallelism. 

Sometimes there occur larger and more irregular foldings, 
windings, and contortions of the texture, but these are fre- 
quently very parallel in their main direction. E. g. at Schwarz- 
enbach, near Hof in the Fichtelgebirge. 

(d) MICA-SCHIST WITH WOOD-LIKE OR \ Or as if the different par- 

COARSELY FIBROUS TEXTURE. I tides had been elongated 

GEOTRECKTER GLIMMERSCHIEFER oder f by stretchino- This pe- 

HOLZGUMMERSCHIEFER. (Germ.) J c il iar textlire is caused by 

a special conformation of the quartz stripped into thin and 

long strips or stalks. 

(e) MICA-SCHIST WITH CONTORTED AND \ The disturbances of the 

IRREGULAR TEXTURE. I parallel texture are partly 

VKUWORREXSCHIEFRIGER oder WULST- r occasioned by external 
GLIMMKUSCIUEKER. (Germ.) ,. , J ,, 

1 TEXTURE FROISSEE ou PUSSES (Fr.)) forces, and partly by 

many tuberous swellings 

of the quartz contained in the rock. Very frequent. 
(/) STRATIFIED MICA-SCHIST. j. Thin seams of mica with slaty 
LAGBNGLIMMERSCHIEFER. (Germ.* cleavage, alternate with fine- 
grained layers of quartz, in which last are sometimes dissemi- 
nated flakes of mica not parallel to the stratification. This 
rock is very characteristically developed near Eger, in Bohemia, 
and between Korbach and Gefrees in the Fichtelgebirge. 
(y) MICA-SCHIST OF KNOTTY TEXTURE. I Small nodules or concre- 
KjfOTENGLiMMERscHiEFER, (Germ.) > tions pervade the mass and 
occasion a knotty texture, disturbing the otherwise parallel 
layers of the mica. Occurs in the Fichtelgebirge, between 
"W alpenreuth and Hiihnerhof. 

Varieties in Composition. 
(A) GARNETIFEROUS MICA-SCHIST. \ Rich in garnets. Ofveryfre- 

(iHANATGLIMMERSCHIEFER. (Germ.) f nll - nf n^n-rpn-p 
MlCASCHIOTE GRENATIFERE. (Fr.) I ^^^ OCCUirCnCC. 

(t) GNEISSIC MICA-SCHIST. I With some felspar in the 

GNEIBSGUMIDJRSCHIEFER. (Germ.)> compound; forms a transition 
state between gneiss and mica-schist. Frequent in the Erzge- 
birge. 

R 2 



244 CRYSTALLINE SCHISTS. 

(K) CHLORITIC MICA-SCHIST. ] With some admixture of chlo- 

CHLORITGLIMMERSCHIEFER. (Germ.) r rite ; forms a transition into 
MICASCHISTE AVEC CHLOMTE. (Fr.) c hlorite-schist. Frequent in 



(/) TALCOSE MICA-SCHIST. ) With an admixture of some talc; 

TALKGLIMMERSCHIEFER. (Germ.) \ forms a transition into talc- 



MICASCHISTE AVEC TALC. (Fr.) j sc hi s t. Occurs in the Alps, 
(m) MICA-SCHIST WITH TWO KINDS or MICA (dark and light- 
coloured). Zschopau in Saxony. 

() GRAPHITIC MICA-SCHIST. \ With admixture of graphite ; 

GRAPHITGLIMMERSCHIEFER. (Germ.) r forms a transition into gra- 

MlCASCHISTE AVEC GRAPHITE. (Fr.) ' 1 



(o) MICACEOUS IRON-SCHIST. \ Forms a transition into 



ElSENGLIMMERHALTIGER GlJMMERSCHIEFER. f femiginOUS Schist. 

(Germ.) ) 

(p) SCHORLACEOUS MICA-SCHIST. ] Forming a transition into 
SCHORLGLIMMERSCHIEFER. (Germ.) I schorl-schist. Eibenstock 
MICASCHISTE AVEC TOURMALINE. (Fr.)) in S axonv> 

(q) HORNBLENDIC MICA-SCHIST. } Forming a transition into 

HORNBLENDEGLIMMERSCHIEFER. (Germ.) I hornblende-schist. E. g. 
MICASCHISTE AVEC HORNBLENDE. (Fr.) J between Goldmiihl and 

Brandholz, near Berneck in the Fichtelgehirge. 
QTJARTZOSE MICA-SCHIST, forming a transition into quartz-schist. 
CALCAREOUS MICA-SCHIST. \ This is either a granular lime- 
KALKGLIMMERSCHIEFER, BLAU- [ stone, very rich in mica, and 
SCHIEFER. (Germ.) ) therefore of fissile texture (ci- 

polline), as it, for instance, occurs in the limestone beds in the 
neighbourhood of Zaunhaus in the Erzgebirge, or it is a rock 
composed of thin alternate layers of mica-schist and granular 
limestone, as is frequently found in the Eastern Alps. 

The following varieties differ in the species of their 
mica : 

(t) PARAGONITE-SCHIST. j The name given by Schafthautl 

PARAGONTTSCHIEFER, Schafthautl. j to certain mica-schist of the Alps 

(Germ.) n -^r^j^ -j^g ordinar mica is 



replaced by paragonite or damourite. To this belongs, e. g., the 
beautiful variety found at St. Gotthard, and is distinguished 
by its containing many cyanites and staurolites. 
(u) AMPHILOGITE-SCHIST. ) The name given by Schaft- 

AMPHILOGITSCHIEFER, Schafthautl. r hautl to the delicate 'flaky and 
(Germ.) somewhat greenish-white mica- 

slate of Zillerthal in the Tyrol, which only contains 40 p. c. 
silica. 

(v) NACRITIDE. j The name given by Schill to a schist oc- 

NACRITID, Schill. j curring at Pike's Peak in Kansas, consisting 
(Germ.) Q f q uar ^ z ^fo bi ac k an( j w hite mica. Per- 

haps it is the same as the Saxon variety described ante (m) . 

Mica-schist is usually more or less stratified or laminated 
independently of and more or less parallel to its schistose 



QUARTZ GROUP. 245 

or foliated texture. Sometimes many different varieties 
alternate and are stratified in thin beds or layers one 
above the other. 

Mica-schist is extensively developed in many mountain 
districts, and there it is usually accompanied by gneiss or 
talc, and chlorite-schist ; it frequently also contains sub- 
ordinate intermediate layers of quartz-schist, hornblende- 
schist, granular limestone, or dolomite, ironstone, or even 
graphite. The distinctly sedimentary formations usually 
overlie the mica-schist, but to this rule there are excep- 
tions, as in the case of gneiss. From its bedding and the 
rocks with which it is usually associated, we must con- 
clude that mica-schist has chiefly been formed by trans- 
mutation from very ancient argillaceous and arenaceous 
deposits. During this process the quartz has undergone 
the least change, the clay has for the most part become 
mica, the superfluous substances in the sedimentary rock 
appearing, as accessory minerals in the mica-schist. A 
clay-slate very poor in quartz might produce a mica- 
schist very rich in mica ; and a clay-slate very rich in 
quartz (or very sandy) might produce a mica-schist very 
rich in quartz. An argillaceous sandstone might perhaps 
produce that variety of mica-schist which forms a tran- 
sition into quartz-schist. If the original rock contained 
lime, then garnet, hornblende, and other minerals might 
also be formed. If the original rock contained subordi- 
nate strata or layers of limestone, ironstone, coal, or the 
like, these would be changed into granular limestone, 
ferruginous mica-schist, graphite, &c. 

We must assume that these processes of transmutation 
have always taken place deep in the earth under the 
influence of great pressure, high temperature, and per- 
haps that they have been aided by the presence of water 
in other words, that they were plutonic or hydro- 
plutonic processes. If there were sufficient alkali in the 
argillaceous deposit, or if alkalies happened to be within 
reach (possibly in a state of solution), then gneiss and not 
mica-schist would be the result. If these hypotheses are 
well founded, they explain the possible mode of formation 
of some mica-schists, which appear to be of considerably 
more recent origin than the greater part of those rocks. 
The process of transmutation may have been hastened in 



246 , CRYSTALLINE SCHISTS. 

these exceptional cases by an extraordinary degree of 
pressure. Cases of this kind are met with in the Alps, 
where between strata of mica-schist certain beds of a 
sandy calcareous composition occur containing distinct 
remains of Belemnites. 

Although mica-schist has been very frequently analysed 
and described, there are but few treatises which make it 
their principal subject. The following describe certain 
special forms of this rock. 

References. 

Beudant and Naumann (the former in Hungary, the latter in 
Scandinavia) have both observed apparent pebbles of quartz 
in mica-schist a circumstance which forcibly suggests a me- 
chanical origin (Naumann's Geognosie, 2nd. ed. vol. i. p. 
527, Anm.). We have also ourselves observed distinct 
pebbles of quartz in beds of limestone lying between parallel 
beds of mica-schist at Jakobeni in the Bukowina. Jahrb. d. 
geol. Keichsanst. 1855, p. 7. 

Schqfthautl, on the peculiar varieties of the Alps, Ann. d. 
Chem. u. Pharm. 1843, p. 733. (Schonfeld and Roscoe, ibid. 
1854, vol. xci. p. 305.) 

Schittj on Nacritide, Ann. d. Chern. u. Pharm. 1857, vol. ciii. 
p. 119. 

24. QUAKTZ-SCHIST. 

QUARZSCHIEFEE. (Germ.) 
QUARTZ SCHISTEUX. (-Fr.) 

A rock chiefly consisting of quartz, but usually contain- 
ing some mica. 

We regard this rock as more or less belonging to the 
mica-schists. It is found to pass over into genuine mica- 
schist through the transition grade of quartzose mica-schist. 

Mineralogically, this rock has greater affinity to the 
siliceous or quartz rocks. Geologically, however, it 
undoubtedly belongs to the metamorphic crystalline 
schists, with which it is usually interstratified in parallel 
but subordinate beds ; and, like the other crystalline 
schists, appears to have originated in metamorphosis of 
sedimentary rocks (probably sandstone). 

We ought, perhaps, on the same principle to include 
some other rocks in the metamorphic series (granular 
limestone, for instance) ; calcspar, however, does not oc- 
cur as an essential ingredient of any crystalline schists, 
whereas quartz is contained in most, and we must con- 



QUAETZ GROUP. 247 

stantly remind our readers that a logically consistent 
system of classification is impossible with rocks. 

We shall again allude to this rock under the head of 
quartz rocks, No. 69 post. 

Varieties in Texture, 
(a) COMMON QUARTZ-SCHIST. \ Consists principally of com- 

CKMKINBB QUARZSCHIEFER. (Oerm.) [ pac t imperfectly - foliated 

QUAIO* scm^x COMMUN. (/v.) ) U it 'e qua rtz, containing only 

little mica; sometimes with very distinct parallel elongations. 

Occurs in the gneiss of Freiberg. 

(6) GRANULAR QUARTZ-SCHIST, j Fine-grained, resembling sand- 

or QUARTZITE. I stone. 

QPARZIT. (Germ.) Jukes says, l Quartz rock or 

> quartzite is a compact fine-grained 

but distinctly granular rock, very hard, frequently brittle, 
and often so divided by joints as to split in all directions 
into small angular, but more or less cuboidal, fragments. The 
colours are generally some shade of yellow, passing occasionally 
into red, and at other times into green. When examined with 
a lens it may be seen to be made of grains, which appear some- 
times as if they had been slightly fused together at their edges 
or surfaces, and sometimes as if imbedded in a purely siliceous 
cement. This cementation or semi-fusion of the grains shows 
at once that it is a sandstone which has been altered and in- 
durated by the action either of heat alone or of heat and water.' 

25. ITACOLUMITE. 

ITAKOLUMIT. (Germ.) 
ITACOLUMITE. (Fr.) 

A fine-grained and at the same time schistose compound 
of quartz with some mica, talc, or chlorite. In thin 
plates it is sometimes flexible. 

This rock first received its name from Von Eschwege. 
Its principal mass consists of grains of quartz, and re- 
sembles a sandstone. The grains of quartz, however, are 
bound together by thin crystalline Iamina3 of mica, 
chlorite, or talc, and these often assume a parallel arrange- 
ment and form thin seams through the rock. Thus its 
foliated texture is occasioned, and the somewhat elastic 
properties of the mica, chlorite, or talc occasionally give 
a flexibility to thin layers or plates of the rock. But not 
all varieties of itacolumite are flexible. The prevailing 
colour of the rock is yellowish ; sometimes, however, it 
has a white-reddish or bluish-grey colour. 

As subordinate ingredients, there occur in it mica- 



248 CKYSTALLINE SCHISTS. 

ceous iron, magnetic iron-ore, martite, native gold, and 
even diamond. The quartz also occurs locally in the 
form of rounded stones or pebbles enclosed in the rock's 
mass, showing clearly the mechanical arenaceous or con- 
glomeratic origin of the rock. If the specular or magnetic 
iron-ores occur in considerable quantity, then a transition 
takes place into ferruginous mica-schist or itabirite (vide 
post, No. 62 K) ; and if the quartz be altogether pre- 
dominant, into quartz-schist (No. 24). 

We may take it as proof of the variable character of 
this rock that it has received many different names. 
Alexander von Humboldt called it itacolumite or quartz 
chloriteux ; Clausen termed it gres rouge, micaschiste 
quartzeux, and gres itacolumite ; Von Martius, elastischer 
Sandstein (elastic sandstone), Quartz-schist and Gelenk- 
quarz (articulated quartz) ; Walchner, quartzose talc- 
schist ; Jacquemont, gres schisteux ; Shepard includes it 
under the head of mica-schist ; Tourney terms it quartz 
rock or the f quartz of the mica slate? and indicates that 
it may be a hornstone ; Yan Uxem even appears to have 
considered it in South Carolina as a variety of Greissen. 

Jukes describes Itacolumite as being a genuine un- 
altered sandstone, more or less micaceous like other sand- 
stones, but the mica in worn spangles, not in connected 
flakes. 

Varieties. 

(a) COMMON ITACOLTTMITE. \ Firm, not flexible, resembling a 
GEMEINER ITAKOLUMIT. (Germ.) L fi rm and somewhat fissile sand- 

ITACOLUMITE COMMTJN. (Fr.) ) 



(6) FLEXIBLE ITACOLUMITE. . Usually very fine-grained, and 



j? thin lars or Plates-very 
flexible. 
(c) CONGLOMERATIC ITACOLUMITE. , ^ , . , , , 

CONGLOMERATARTIGER ITAKOLUMIT. (Germ.)\ Enclosing rounded peb- 
ITACOLUMITE GRENu. (Fr.) ( bles of quartz. 

Yon Eschwege informs us that in the Brazils itaco- 
lumite forms whole systems of strata of great thickness, 
extending for several hundred miles in length. The 
mountain Itacolumi, near Villa Eica (5,400 feet high), 
consists almost entirely of this rock. Shepard and 
Lieber found it very extensively developed in North 
and South Carolina, where it generally lies between lime- 



CHLORITE, ETC., GROUP. 249 

stone and clay-slate, and contains subordinate layers or 
beds of talc-schist, ferruginous mica-schist, itabirite, ca- 
tawbarite, and fine-grained limestone. Von Helmersen 
and Hofmann also found the rock in the Ural Moun- 
tains ; Von Eschwege in Portugal ; Schulz in Spain ; 
Gergens in the slate region of the Rhine. 

References. 

v. Eschwege. Beitr. z. Gebirgskunde von Brasilien, 1832, p. 174. 
O. Lieber, Gangstudien, vol. iii. p. 323. 
Shepard, Report of South Carolina, 1854. 
Schuh, Bullet, de la Soc. ge*ol. de la France, 1834, p. 416. 
Gergens, in v. L. u. Br. Jahrb. 1841, p. 566. 
Lucas (as early as 1815) found diamonds in it in the Brazils. 

Nouveau dictionnaire d'hist. nat., art. Diamant. The same 

fact was confirmed by Heusser and Claraz, in the Zeitschr. 

d. d. geol. Ges. 1859, vol. xi. p. 448. 
r. Hnmboldt. Gisement des Roches dans les deux Hemispheres. 

p. 89. 

v. Martius, Reise in Brasilien, vol. ii. 
Clausen, Bullet, de 1'Acad. de Bruxelles, 1841. 
Walchner, Handbuch d. Geognosie, p. 38. 
Tourney, Report on the Geology of South Carolina, 1848, p. 6. 
Jacquemont, Voyage dans 1'Inde. 

CHLORITE, TALC, AND HORNBLENDE GROUP. 

These rocks have been severally termed Chlorite-schist, 
Talc-schist, and Hornblende-schist, from the prevalence of 
those respective minerals in their composition. 

In their chemical composition they resemble the basic 
rather than the acidic igneous rocks ; that is, they contain 
more magnesia and lime, and, for the most part, less silica 
than the acidic rocks. 

They occur as subordinate beds in the mica-schist, or 
they entirely take the place of mica-schist in some for- 
mations. 

Serpentine might also be included in this group, by 
reason of its chemical and frequently also its geological 
character. Nevertheless, inasmuch as serpentine often 
occurs under other and very different geological rela- 
tions (appearing as the product of igneous rocks), we 
prefer to class that rock separately amongst the special 
rock formations. 

By introducing this group of rocks between the mica- 
schists and the argillaceous mica-schists, we interrupt a 



250 CRYSTALLINE SCHISTS. 

connected series of transition between those two groups, 
but such interruption only represents similar inter- 
ruptions actually occurring in nature. 

26. CHLOKITE-SCHIST and POTSl?ONE. 

CHLORITSCHIEFER imd TOPFSTEIN. (Germ.) 

SCHISTE CHLORITIQTJE. (Fr.} 

A schistose aggregate of chlorite, usually combined with 
quartz, sometimes also with felspar, mica, and talc. 
It has a greenish colour and scaly appearance. 

Spec. grav. . ? ',''- ~- . r V 2-7 2-8 
Contains silica V . \ /. * ' 31 42 p. c. 

The principal mass of this rock is composed of chlorite 
of green or blackish-green colour and greyish-green 
streak. It is usually of coarsely foliated texture and soft. 
The quartz sometimes transfuses the whole mass, and so 
makes the rock hard ; sometimes it only occurs in the 
form of thin scattered lamina?, lenticular or irregular 
swellings ; sometimes again it traverses the rock in thin 
veins. Felspar, mica, or talc are only occasionally to be 
distinctly recognised as ingredients ; many other minerals 
are, however, found as accessories, and often in very per- 
fectly formed crystals ; the most frequent of these are mag- 
netic iron-ore, garnet, talcspar, actinolite, and tourmaline. 

This rock forms transitions into talc-schist, protogine 
gneiss, mica-schist, clay -mica-schist, and slaty serpentine, 
and it often lies in alternate strata with these rocks. It 
is widely spread in the central chain of the Alps, is very 
characteristically developed in the Fichtelgebirge, near 
Schwarzbach, Wiersberg, &c., and also in the Eastern 
Carpathians. It very often contains subordinate beds 
or layers of magnetic iron-ore, ferruginous mica-schist, 
copper and iron pyrites, granular limestone, quartz, &c. 
It is usually very distinctly stratified. 

Chlorite-schist can scarcely be divided into separate 
varieties, which have not found a place under other heads, 
but some analogous rocks may be annexed to it, and may 
almost take the place of varieties. 

(a) THE CHLORITE-SCHIST OF HARTHATT (near Chemnitz). The 
principal mass of this rock consists of an imperfectly foliated 
chlorite-schist of dark-green colour, traversed by many layers 
and veins of quartz. Numerous very distinct yellow spots appear 



CHLORITE, ETC., GROUP. 251 

prominently arranged in certain zones. These were for a long 
time taken to be flakes of talc. A. Knop has, however, ana- 
lysed this rock more narrowly, and discovered that the spots 
do not consist of talc, but mostly of a yellowish-green micaceous 
substance, a kind of pinite, which, however, itself appears 
to be a product of transmutation from oligoclase (or labra- 
dorite), and in many places has preserved its crystalline form 
and distinct cleavage. Strange to say, these felspar crystals, in 
the process of their transmutation into aggregates of mica, 
have even changed their outward shape, and accommodated 
themselves somewhat to the foliated texture of the rock. This 
rock frequently contains some pyrites, brownspar, and titanic iron 
as accessories/ It divides into plates or wood-like fibres. It forms 
subordinate beds in the clay-mica-schist of the same district. ^ 

(6) CHLORITOID SCHIST is the name given by Hunt to a certain 
dark-coloured schist, very extensively developed in Canada, 
principally consisting of chloritoid, a mineral closely allied to 
chlorite, and also to ottrelite. 

(c) POTSTONE. \ Consists of a felt-like web of chlorite ; 

LAVKZOTEIN, it is only rarely foliated. Specific gra- 
I vity, 2-8 (?) ; content of silfca, 30-60 
) p. c. (?) The mass is greenish-grey to 
blackish ; its streak greenish-white. It is soft, sectile, and 
quite infusible. It sometimes contains mica, calcspar, dolo- 
mite, and magnetic iron-ore or iron pyrites scattered through 
its mass, and hence it sometimes effervesces on the applica- 
tion of acid. In fire it loses 7'21 per cent, of its weight, pro- 
bably in consequence of the large quantity of water which it 
contains (sometimes as much as 11 per cent/). 

This rock is easily manufactured into firebricks and fire- 
proof utensils. It is found in very characteristic form in the 
Alps, together with serpentine as a subordinate stratum in 
chlorite-schist, and it forms transition states into serpentine 
Chiavenna, Drontheim in Norway (?), Boston in Massachusetts, 
Potton in Canada. 

References. 

Varrentrapp, Poggend. Annalen, 1849, vol. xlviii. p. 189. 
Knop, Progr. der Chemnitzer Gewerbschule, 1856. (?) Neues 

Jahrb. f. Min. 1863, p. 808. 

finish, on Chloritoid Slate, v. Leonhard's Jahrbuch, 1861, p. 574. 
Delesse (Potstone), Bullet, de la Soc. ge*oL de France, 1857, [2] 

vol. xiv. p. 281. 
Studer (Potstone), Bibl. univers. de Geneve, 1856, [4] p. 213. 

27. TALC-SCHIST. 

TALKSCHIEFER. (Germ.) 

TALCSCHISTE (STEASCHISTE, Brongniarf). (jFV.) 

A schistose aggregate of talc, usually combined with some 
quartz or sometimes with felspar, yellowish or greenish 
colour and soft greasy feel. 



252 CRYSTALLINE SCHISTS. 

Spec, grav 2-62-8 

Contains silica 50 57 p. c. ; at Zebernick, in Hungary, only 
27-6 j at Hinterbriihl, even 62-1. 

The principal mass of these rocks consists of talc, of 
light-yellow, yellowish-green, or greenish-grey colour, 
with a mother-of-pearl varying to resinous lustre. As 
it contains less silica than the mineral talc (which has 64 
per cent.), we may infer that some chlorite enters into its 
composition. 

It contains little quartz ; and only in grains, flat lenti- 
cular particles, laminae, or irregularly shaped masses, or 
irregular veins, all subordinate as to size and quantity. 

Felspar is only to be seen in delicate particles scattered 
here and there ; it is not more frequent than several of 
the following accessory minerals : chlorite, mica, talcspar, 
garnet, actinolite, asbestos, magnetic iron-ore, and iron 
pyrites. This rock forms transitions into chlorite-schist, 
clay-slate, mica-schist, and protogine-gneiss. 

Varieties, 
(a) COMMON TALC-SCHIST. ] Not unusual in the Alps. At 

GEMEINER TALKSCHIEFER. (Germ.) [ Ochsenkopf, near Schwarzen- 
TAX.CSCHISTE COMHUN. (Fr.) j berg ^ the Erzgebirge, a 

variety (with corundum) occurs imbedded between strata of 
mica-schist. 

(6) LISTWENITE is the name which has been given to a variety in 
the Ural Mountains, which contains much quartz combined 
with talcspar or calcspar, and from that combination assumes 
a somewhat granular slaty texture. The same rock, at Bere- 
sowsk is displaced and penetrated by veins of Beresite, which 
are again penetrated with quartz veins containing some gold. 

(c) DOLERINE is the name given by Jurine to a talc-schist with es- 
sential ingredients of felspar and chlorite, and according to 
Favre this rock is extensively spread in the Pennine Alps. 

Talc-schist is almost always stratified, and forms alter- 
nating beds with other crystalline schists. 

References. 

G. Rose, on Liswanit, Reise n. d. Ural, vol. ii. p. 537. 
Jurine, on Dolerine, in the Journ. des Mines, vol. xix. p. 374. 
Favre, on Dolerine, in v. L. u. Br. Jahrb. 1849, p. 41. 
Scheerer, Analyse des Talksch. von Fahlun, in Poggend. Ann. 

1851, vol. Ixxxiv. p. 345. 
Richter, Anal. d. Talksch. von Gastein, in Poggend. Amu 1851, 

vol. Ixxxiv. p. 368. 



CHLORITE, ETC., GROUP. 253 

Ferjentsik, Anal d. Talksch. v. Zebernick, in Jahrb. d. geol. 

Reichsanst. 1856, p. 807. 
Raysky, Anal. d. Talksch. v. Hinterbriinl, in Jahrb. d. geol. 

Reichsanst. 1854, p. 642. 

28. HORNBLENDE-SCHIST and HORNBLENDE 
ROCK. 

HORNBLENDESCHIEFER und HORNBLENDEFELS, AMPHIBOLTT. 

(Germ.) 
SCHISTE AMPHIBOLIQUE et AMPHIBOLITHE, Brvngniart. (Fr.) 

A schistose or fine-grained to compact rock, consisting 
chiefly of hornblende, combined with small quantities 
of felspar, quartz, or brown mica. Always dark-green 
to black. 

Spec, gray , 3 3'1 

Contains silica ..... 48 54 p. c. 

This rock is most usually of foliated texture. Its prin- 
cipal mass is granular and sometimes also fibrous, and 
consists of common dark-green hornblende as its principal 
ingredient, with which some felspar, quartz, or mica is 
usually combined. If the latter are present in considerable 
quantity, then transitions take place into diorite (6), dio- 
rite-schist (No. 6 a), or syenite-gneiss (No. 22). As 
accessories there also occur garnet, pistacite, iron pyrites, 
magnetic iron-ore, &c. 

The varieties of prevailing schistose character are usu- 
ally imbedded between strata of other crystalline schists, 
to which they clearly belong, and into which they pass 
over by grades of transition. 

They also sometimes pass into rocks not of a fissile tex- 
ture, such as hardly can be classed with the argillaceous 
schists, and which may perhaps be of igneous (eruptive) 
origin, especially as they form transitions into diorite. 

Varieties of Texture. 

(a) HORNBLENDE-SCHIST. ] Usually thickly foliated, and at 

HoRNBLENDisscHiEFEB. (Germ.) L the same time fibrous : this tex- 
SCHIKTK AMPHXBOLXQUE. (Fr.) J ture being ^j^ V ^ pft _ 

rallel position of fibres of hornblende of various thickness. 
Quartz and felspar occur as a part of the compound of the 
principal rock, but also in nests or veins. This rock is often 
found (subordinate) in strata of gneiss, mica-schist, and 
<-lil< rite-schist ; e. jr., Miltitz, near Meissen, and the district of 
Munchberg in the Fichtelgebirge. 



254 CEYSTALLINE SCHISTS. 

At Hanover in North America hornblende-schist is found, 
containing large dodecahedrons of garnet. 

(6) HORNBLENDE EocK. ] Without fissile texture. E. g. in 

HORNBLENDEFELS. (Germ.) \ the district of Hof in the Fichtel- 
AMPHIBO. ^ J gebirge. 

Variety in Composition. 

(c) ACTINOLITE-SCHIST. \ Chiefly consisting of actinolite, and 

STRAHLSTEIN oder ACTING- (therefore entirely fibrous, otherwise 
LITHSCHIEFER. (Germ.) f . , ,., , ,, J-. -. . , ' -^ 

J just like hornblende-schist. Found to 

the south of Oberwiesenthal in the Erzgebirge ; also at Clau- 
sen in the Tyrol. 

We might also include eklogite (No. 44) under this 
head, but as it is at least doubtful if its origin be that of 
the metamorphic schists, and as it belongs to the rocks of 
exceptional character, and by 'reason of its richness in 
garnets may be conveniently placed with the other garnet 
rocks, we have so classed it. 

References. 

Eischof's Geologie (1st edition) contains almost the only de- 
tailed account of hornblende-schist. See II. p. 130. 
On actinolite-schist, see Reuss in v. L. u. JBr. Jahrb. 1840, p. 41. 

SCHISTS INDISTINCTLY CRYSTALLINE. 

These form the connecting link between the extreme 
metamorphic crystalline schists (especially gneiss and the 
mica-schists) and the clay-slate and slate-clay rocks, 
which latter being much less changed are still distinctly 
sedimentary. We therefore term them argillaceous mica- 
schists. 

29. ARGILLACEOUS MICA-SCHIST, PHYL- 

LITE. 

THONGLIMMERSCHIEFER, PHYLLIT, URTHONSCHIEFER. (Germ.} 
PHYLLADE, D'Aubuissoti. (Fr.} 

A schistose aggregate in which mica is usually to be recog- 
nised as the chief ingredient^ or in which the peculiar 
structure of mica rocks is apparent. Sometimes the 
whole mass appears homogeneous, differing only from 
clay-slate by its superior lustre. 

Spec, grav 2-62-8 

Contains silica . . . . 45 74 p. c. 

Argillaceous mica-schist is but a transition state between 



ARGILLACEOUS MICA-SCHIST. 255 

mica-schist and clay-slate, as is apparent from its passing 
over into both these rocks. We might term it an imperfect 
mica-schist or a very much transformed and somewhat 
crystallised clay-slate. Its chemical analysis also agrees 
with this definition. But its chemical composition varies 
as much as that of mica-schist or clay-slate. Its principal 
ingredients are always quartz and mica (or some mineral 
of the same character as mica), but the quantitative pro- 
portions of these ingredients are very different in different 
rocks. With these principal ingredients are associated 
chlorite, talc, felspar, hornblende, garnet, &c., which occa- 
sion transitions into chlorite-schist, talc-schist, hornblende- 
schist, and gneiss. 

The colour of these rocks is usually grey, greenish, or 
bluish-grey, but sometimes yellowish, reddish, brownish, 
and violet. Their lustre varies between the mother-of- 
pearl, the silky, and the half metallic. They always have 
a distinctly fissile texture, but not by any means a perfect 
cleavage. Sometimes they show fine parallel foldings, or 
sometimes there occurs a second fissile texture obliquely 
traversing the principal direction, occasioning a rough 
fibrous cleavage. When the slaty cleavage is perfect, it 
is usually not parallel to the stratification. 

In the apparently homogeneous principal mass, we dis- 
cover grains or irregular lenticular swellings or masses 
of quartz, or else veins of quartz or flakes of mica (or 
sericite), chlorite, talc, hornblende, felspar, chiastolite, 
andalusite, iron pyrites, magnetic iron-ore, or graphite. 
When these minerals are considerable in quantity, there 
arise varieties in composition. But these varieties are 
not peculiar to this rock ; they are necessarily repeated in 
mica-schist, as well as in clay-slate. 

Varieties in Texture. 
(a) COMMON ARGILLACEOUS MICA-SCHIST. 

IKINKK THOXGLIMMERSCHIEFKR. (Germ.) 
PHYLLADB COMMUN (SATIXE). (Fr.) 

(6) FOLDED OR CONTORTED. 

I.IKTKR THOXGLIMMERSCHIEFER. (Germ,) 

(c) FIBROUS OR WOODY TEXTURE. 

HOLZARTIGER THOXGLIMMERSCHIEFER. (Germ.) 

(d) VERY MUCH CONTORTED. 

SKHR VERWORREX SCHIEFRIGER oder WULSTIGER THOXGLIMMERSCHIEFER. 

(Germ.) 
PUBSE, FROIS8E. (Fr.) 



256 CRYSTALLINE SCHISTS. 



0) NODULAR SCHIST. j Which we also enumerate below, as 

(} * a iet ? in comosition. 



a iet ? in compositi 

Varieties in Composition. 
(f) RICH IN MICA. \ 

Gu ?R. T So M ' Transition into mica-schist. 

MICACE. (/>.) 



Forms transitions into quartz. 

SCHIEFKR. (Germ.) schist. 

QTJARTZEUX. 

(A) CH CHZmscH E H THoxGUMMEB-l Fo n ? transitions into chloritic 

SCHIEFER. (Germ.) SChlStS. 

CHLORITIQUE. (Fr.) 
(t) TALCOSE. ) 

TALKIGER THONGLQIMER- I Forming a transition into talc-schist. 

SCHIEPER. (Germ.) 
TALQUEUX. (Fr.) 

(k) A VARIETY CONTAINING HORNBLENDE. 

HORNBLENDEHALTIGER THONGLIMMERSCHTKFER. (Germ.) 

(I) A VARIETY CONTAINING FELSPAR. x Form i nff a transition 
FELSPATHHALTIGERTHONGLIMMERSCHIEFER. I J 

(Germ.) j into gneiss. 



. 

(6?erm.) j into garnet-mica-schist. 

GRENATIFERE. (/V.) / 

(w) SERICITE-SCHIST. ] The name given by List to a variety 

SERICITSCHIEFER. (Germ.) Iwhose principal mass consists of seri- 
SCHISTEASERICITE. (j fr.)) cite ( green m i cace ous mineral, re- 
sembling damourite, with a silky lustre, see ante, p. 23), and 
which usually also contains quartz and felspar (albite according 
to List). The colour of this rock in the Taunus, where it is 
very extensively developed, is greenish with green and yellow 
spots, or violet. It is often penetrated by veins which contain 
quartz and albite. The very considerable quantity of alkalies 
which it contains, especially of potash, is remarkable. List 
further distinguishes three sub-varieties, according to their 
colour. 

(a) Violet, very soft, with thin slaty cleavage. Spec. grav. 

2-88. 

(j8) Green, harder, with thick slaty cleavage (folded), with 
little albite, and a microscopic quantity of magnetic 
iron-ore. Spec. grav. 2-79. 
(y) Spotted, soft ; often decomposed j with much albite and 

quartz. Spec. grav. 2-68. 

(o) OTTRELITE-SCHIST. ] The principal mass foliated, and usually 

OTTRELITSCHIEFER. (Germ.) I grey. It contains greenish laminae of 

SCHISM loirsft. (/v.) Jott^^te. This variety is frequently 

found in the Ardennes. It has also been discovered by Giim- 

bel in the district of Ebnat in Bavaria. 

(p) CHIASTOLITE-SCHIST. \ The mass is slaty, and usually 

CHIASTOUTHSCHIEFER. (Germ.) ( dark-coloured. It contains many 
SCHISTE MACI^ERE. (Fr.) j crygtals of cMastolite disseminated 



ARGILLACEOUS MICA-SCHIST. 257 

through it in the most opposite directions. The chiastolite- 
schist (which also forms a variety of clay-slate) is found on 
the contact margins of plutonic igneous rocks, e. g. next to 
irranite. Near Gefrees in the Fichtelgebirge. Also abundant 
about Skiddaw, Cumberland. 

(q) No DULAR or SPOTTED SCHIST. \ This schist contains small con- 
KNOTENSCHIEFER, FLECK- oder cretions of different structure, 
ScHS C xo^SS R ou ((7 ^^. hardness, and colour to that of 
(Fr.) J the general mass. They are, for 

the most part, harder and darker, and they either form small 
knots or only spots with indistinct margin ; sometimes they 
resemble the currants in a fruit-pudding, hence their different 
names. Their composition has not vet been determined with 
accuracy by the various mineralogical chemical analyses which 
they have undergone, according to which they have been suc- 
cessively taken for a kind of fahlunite, for hornblende, serpen- 
tine, chiastolite, or andalusite. It is very possible that at 
different places they are somewhat differently composed. In 
reference to their origin, it is of special interest that according 
to the careful investigations of Carius, the schist with nodules 
does not differ in the quality or proportionate quantity of its 
ingredients from the same schist without nodules farther re- 
moved from the contact, so that no new substance appears to 
have been added to form those concretions, but they appear 
rather to have arisen from a new arrangement of the previously 
existing ingredients. At the margin of the granite in the 
AVestern Erzgebirge and Voigtland, these nodular schists are 
very frequent, and are observed there just as much in the clay- 
mica-schist as in the ordinary clay-slate. A similar appearance 
occurs at Wechselburg in Saxony, in a rock which is decidedly 
mica-schist. 

(r) ALUM-SCHIST. \ This schist contains much carbon, and 

ALAUNSCHIEFER. (Germ.) I i s thereby rendered black. Pyrites is 
semen ALUMIXEUX. (Fr.) j alwayg mixed with it in fine particles, 
through whose decomposition alum and iron- vitriol are formed. 
In the case of this variety, we can only decide from the 
bedding whether it belongs to argillaceous mica-schist or tq 
clay-slate, for the carbon which it contains thoroughly oblite- 
rates the slender landmarks by which the difference might 
otherwise be established. It is characteristic of most of the 
alum-schists, that they are of very much contorted or displaced 
texture, and are frequently pervaded by irregular swollen- 
shaped fragments of quartz and lustrous but bent laminae 
(mica), and sometimes also lenticular concretions of bitu- 
minous limestone or anthraconite. lieichenbach in Voigtland. 

(s) CARBONACEOUS SCHIST, BLACK CHALK. ] In the case of this 
ZKICHNENSCHIKKER, SCHWARZE KREIDE. (Germ.) I yarietv verv rich in 

J carbon, we can only 

determine by its bedding whether it belongs to argillaceous 
mica-schist or to clay-slate. It is a quartzless and very soft 
slate, which, from admixture of carbon, is of a black colour, 
and also imparts a black streak, so that it may be used for 
S 



258 CRYSTALLINE SCHISTS. 

drawing or writing. Ludwigstadt in the Thuringian Forest, 
where it belongs to clay-slate. 

All the above-mentioned varieties in composition are 
equally applicable to the ordinary clay-slate as to the 
argillaceous mica-schist, and we shall therefore have to 
enumerate them again when we come to consider that 
rock, but our previous descriptions will suffice for both. 

Argillaceous mica-schist is usually also distinctly stra- 
tified in addition to its foliated texture, which, as already 
said, is not parallel to the stratification ; otherwise, as to 
its bedding and extent, it exactly resembles mica-schist, 
with this only difference, that it more usually than that 
rock is interstratified with the oldest sedimentary and dis- 
tinctly fossiliferous rocks. 

By the name of argillaceous mica-schist we do but 
seek to establish a stage of transmutation between clay- 
slate proper and mica-schist. 

References. 
Frick, Pleischl, Sauvage, and Kjeridf have contributed various 

analyses to Poggend. Ann. 1835, vol. xxxv. p. 188 ; in the 

Journ. f. prakt. Chemie, 1844, vol. xxxi. p. 45 ; and 1855, 

vol. Ixv. p. 192. 
List, on Sericitschiefer, in the Jahrb. d. Vereins f. Naturk. in 

the Duchy of Nassau, 1850, No. 6, p. 128. 
Lipold, on Sericitschiefer in the Alps, Jahrb. d. geol. Keichs- 

anst. 1854, pp. 201 and 359. 
Giimbel, on Ottrelitschiefer, inCorresp.-Bl. d. zool. mineral. Ver. 

z. Regensburg, 1853, p. 53, and on Phyllit, in the same, 

1854, p. 12. 

Naumann, on Knotenschiefer, Erlauter. z. geogn. Karte v. Sach- 
sen, 1838, No. II. p. 264, and 1845, No. V. p. 50. 

Kersten, on Knotenschiefer, in Journ. f. prakt. Chemie, vol. xxxi. 
p. 108. 

Carius, on Knotenschiefer, in the Annalen d. Chemie. u. Pharm. 

1855, vol. xciv. p. 45; and in v. L. u. Br. Jahrb. 1856, 
p. 595. 

Miiller, on Knotenschiefer, in the Berg- u. Hiittenm. Zeitung, 

1858, p. 107. 
Durocher, on Chiastolith and Knotenschiefer, in Bullet, de la 

Soc. geol. de la France, 1846, vol. iii. p. 546. 



259 



CHAPTER III. 

SEDIMENTARY AND FRAGMENTAL ROCKS. 

ALL sedimentary rocks are stratified ; or at least, their 
beds lie one above the other in parallel planes. The 
greater part consists of the debris of older rocks mechani- 
cally washed together and deposited from a state of sus- 
pension in water. A few only are the result of chemical 
precipitate of mineral substances. Many contain organic 
remains (fossils) more or less distinct ; some consist entirely 
of such. 

As a consequence of their origin, the sedimentary rocks 
are rarely of genuine crystalline conformation. Some, 
however, which appear to be actual chemical precipitates 
from aqueous solutions, such as gypsum and rock-salt, 
usually possess a crystalline structure. 

Following the different origin of these rocks, we may 
divide them into 

(a) Mechanical deposits. 

(b) Chemical precipitates. 

(c) Rocks resulting from organic processes. 

(a) Phytogenic, caused by the accumulation of vege- 
table matter. 
($) Zoogenic, caused by the accumulation of animal 

remains. 

The minerals which chiefly predominate in sedimentary 
rocks are not the same as those which are most abundant 
in the igneous and the metamorphic rocks. We find in 
the sedimentary rocks little or no felspar, hornblende, or 
pyroxene. The following are those which occur with 
greatest frequency : Quartz, which in general terms we 
may call the most abundant mineral of the earth ; clay 
(itself, however, a compound rather than a distinct mine- 
ral) ; carbonates of lime and magnesia, as calcspar (lime- 
stone) and dolomite ; sulphate of lime, as gypsum and 
anhydrite ; chloride of sodium, as rock-salt ; finally, coal 
and iron-ores. 

Gypsum (or anhydrite), salt, coal, and iron, usually 
form distinct and separate beds of comparatively small 

8 2 



260 SEDIMENTARY ROCKS. 

extent : the principal and most important sedimentary 
rocks are composed chiefly of the first-named of the above 
minerals, quartz, clay, and carbonate of lime (or magne- 
sia). They may be accordingly divided into argillaceous 
rocks, calcareous rocks, and quartzose rocks. The marl 
rocks occupy an intermediate place between the calca- 
reous and argillaceous. The quartzose rocks may be 
divided into the arenaceous or sandstones, and the con- 
glomerates, to which we may add certain other fragmental 
rocks containing less quartz, usually termed tufa or tuff. 

The material for all these several rocks was mostly 
derived from the disintegration of more ancient previously 
existing rocks. The igneous rocks, by the decay of their 
felspar, hornblende, augite, and mica, have supplied the 
following substances towards the formation of the sedi- 
mentary rocks : argillaceous mud, and weak solutions 
of lime, magnesia, silica, potash, soda, oxide of iron; 
their quartz has furnished grains of sand ; in some cases 
their mica has remained undecomposed, and is found as 
mica in minute Iamina3 in the sedimentary rocks. The 
older sedimentary rocks have also in process of time be- 
come disintegrated, and have furnished similar materials 
to form the more recent, and every solid rock has at times 
furnished pebbles, and other fragments for the formation 
of conglomerates. 

The several sedimentary deposits have been divided 
into so-called formations, according to the order of their 
superposition, and consequently of their age, and these 
again have been gathered into groups, which answer to 
longer periods of deposit. 

It may therefore be useful here to present the following 

TABLE OF GEOLOGICAL PERIODS.* 

C Recent Formations of every kind. 

'^ | Mud, sand, gravel, calcareous and volcanic tuff, coral reefs, 

bog iron-ore, turf, peat, &c., guano, infusorial beds. 

Pleistocene) or Post-Pliocene Formation. 

Diluvial or glacial deposits, loam and breccias of bone- 
caverns, brick-earth and fluviatile loam or loess, valley 
gravels, bog iron-ore, calcareous tuff, coral-reefs, &c. ' 



1! 



* In different countries these are somewhat differently divided and 
named. 






SEDIMENTARY ROCKS. 



261 



ENGLAND. 

Pleiocene Formations. 

Red and coralline crag. 

Miocene Formations. 
Absent in England. 

Eocene Formations. 

Fluvio-marine strata of Isle of 

Wight and Hampshire. 
Bagshot series. 

London clay and Bognor beds. 
Plastic clay or Woolwich and 

Reading beds. 
Thanetbeds. .f 

Cretaceous Formations. 

White chalk with flints. 
White chalk without flints. 
Chalk marl. 
Upper greensand. 
Gault. 

f Lower greensand or neocomian. 
\ Speeton clay. 

Wealden beds, weald clay, and 
Hastings sand. 

Oolitic or Jurassic Formations. 
Purbeck beds. 
Portland beds. 
Kimeridge clay. 

Coral rag. 

Oxford clay. 

Cornbrash. 

Forest marble and Great or 

Bath oolite. 
Fullers' earth. 
Inferior oolite. 
Upper lias sand and clay. 
Marlstone or middle lias. 
Lower lias clay and limestone. 

Triassic Formations. 

Penarth or Rhsetic beds. 
Dolomitic conglomerate. 
Red marls -with rock-salt and 

gypsum. 
White and brown sandstones 

(waterstones) . 
Red and mottled sandstones, 

pebble-beds of conglomerate. 



GERMANY. 

Aralo-Caspian deposits. 

Molasse formation of the Alps 
Tegel, near Vienna. 

Browncoal formation in North 
Germany. 

Nummuliten formation. 
Flysch formation. 



Maestricht beds. 

Turonien, quadersand, planer. 
Cenomanien. 
Albien, aptien. 
Hils-formation. 

Deister formation. 



White Jura. 

Lithographic slate of Solen- 
hofen. 



Brown Jura. 



Black Jura. 



Keuper. 

Koessen or Upper St. Cassian 
beds. 



Muschelkalk (absent in Eng- 
land. 
Buntsandstein. 



262 



SEDIMENTARY JIOCKS. 



ENGLAND. 

Dyas or Permian Formations. 

Red marls and magnesian 

limestone. 
Lower sandstone. 

Carboniferous Formations. 
Coal-measures. 
Millstone grit. 
Carboniferous limestone 
Lower limestone shale. 



GERMANY. 



Zechstein formation. 

Kupferschiefer. 

Rothliegendes. 



Steinkohlen formation. 

Flotzleerer sandstein. 
Kohlenkalkstein. 
Kohlen formation of Hai- 
nichen, or kulm. 



Devonian Formations {Old Red Sandstone). 



Dartmouth slate group. 
Plymouth group. 
Liskeard or Ashburton 

group. 
Old red sandstone. 



Cypridinenschiefer, or 

Kramenzelstein. 
Str5ngocephalen-Kalk. 
Calceolaschiefer. 
Spiriferen-Sandstein and 

Schiefer. 



Silurian Formations. 

Ludlow group "j 

Wenlock group > 

May hill group J 

Lower Llandovery beds 1 

Caradoc sandstone and Bala beds I 

Llandeilo flags 

Lingula flags 

Cambrian Formations. 

Gritstone, sandstone, and slate, with few or no organic 
remains. 

Laurentian rocks of Canada and the north-west of Scotland. 

Below the sedimentary rocks are usually found the 
crystalline schists. 

The entire series of formations is, however, never to be 
found in any one locality. 

The mere geological age of deposit does not inform us 
of the nature of the rock, nor can we, on the other hand, 
from the petrographic character arrive at its geological age. 
Both attributes are to a certain extent independent of each 
other. No kind of rock is restricted to any particular 
period, and although there exist some very general differ- 
ences between the rocks of recent and ancient deposit, yet 
even these do not prevail universally. 



ARGILLACEOUS GROUP. 263 

ARGILLACEOUS GROUP. 

The argillaceous rocks were originally nothing but 
sediments of clayey mud, with some admixture of fine 
quartz-sand, flakes of mica, hydrated oxide of iron, and 
organic remains. These materials, by a slow process of 
transmutation and mechanical consolidation, have ulti- 
mately become solid rocks, some of them carboniferous or 
bituminous. 

The principal rocks of this group are clay-slate, argilla- 
ceous shale, claystone, clay, and mud or silt (loess), with 
their several varieties. To these we must also add the 
marl rocks. 

To arrange these rocks according to the order of their 
origin and development, we should begin with the clay 
and loess, from which (perhaps by the simple agency of 
pressure) claystone, argillaceous shale, and clay-slate have 
been successively formed ; the several varieties of these 
rocks being occasioned by the accessory admixtures con- 
tained in the original compound. 

In the present treatise the order is inverted, and the 
metamorphic rocks having been already described, we most 
naturally pass first to those of the sedimentary rocks which 
are nearest to them, i. e., the most changed, taking the 
newer formations last. 

We cannot draw a sharp distinction between argilla- 
ceous mica-schist, clay-slate, and argillaceous shale, but 
the extreme or ideal development of each of these stages 
of transmutation has a marked character, distinct from the 
others. Characteristic argillaceous mica-schist is still 
somewhat crystalline ; clay-slate is not crystalline, and in 
fracture it is dull, but yet firm, and has a perfect slaty 
cleavage ; characteristic argillaceous shale, on the other 
hand, is soft or flexible, separates along the lamination 
instead of by slaty cleavage, and is more obviously an 
earthy aggregate. Argillaceous mica-schist frequently 
contains various crystalline accessory minerals, but genuine 
clay-slate much more rarely, and of fewer kinds ; argil- 
laceous shale at the most only occasionally contains some 
pyrites. 

30. CLAY-SLATE. 

THONSCHIEFER. (Germ.} 

SCHISTE ARGILEUX, SCHISTE ARDOISIER. 



264 SEDIMENTARY ROCKS. 

A compact fissile rock of a dull blue-grey ', bright red, 
purple, green, or black colour ; consists chiefly of clay ; 
sometimes with accessory admixtures of quartz, mica, 
and other minerals. 

The slaty cleavage is usually very perfect, and only 
occasionally coincides with the original lamination of 
the rock. 

Spec. grav. . '.'".' . ... . 2-52-8 
Contains silica . . .- .. v . 40 75 

The characteristic feature of clay-slate as distinguished 
.from other rocks of the argillaceous group is that its slaty 
cleavage, frequently very perfect, is altogether inde- 
pendent of its original bedding, although in some instances 
(which we may regard as accidental) it coincides with the 
original lamination. Whether this slaty cleavage is due to 
pressure, or to some agency resembling the crystallising 
force which has acted on smaller mineral masses, has been 
a subject of debate since the time of Sedgwick, who first 
called attention to this important phenomenon. It is a 
question which is still unsettled, and which must probably 
so remain for some time longer. 

Varieties in Texture. 

(a) COMMON CLAY-SLATE. ) With perfect or imperfect 

GEMEIXER THONSCHIEFER. (Germ.) L cleavage, very variously CO- 
SCHISTE ARGILEUX OOIUK. (Fr.) J loure( ^ ^ ^ ^ &c _ 

cessory minerals. It contains, e. g., quartz, in irregular masses 
(or swellings), or lenticular masses, or in veins ; pyrites, in 
crystals or nodules, &c. Sometimes its slaty cleavage is much 
distorted. It is very frequent in all districts of the transition 
period (greywacke) in Germany. 

(&) ROOFING SLATE. \ The name given to the purest 

DACHSCHIEFER und TAFEL- |_ varieties of clay-slate, whose cleav- 

SCHIEFER. ((rerm.) t* i t ,1 

SCHISTE ARDOISIER, (Fr.) a g e is very perfect and smooth, 
' allowing of their being split into 

very thin plates, which nevertheless retain a high degree of 
firmness and solidity. A dark- coloured variety, containing an 
admixture of carbon, is termed in Germany Tafelschiefer. 

Roofing slate, with a view to its fitness for the purpose its 
name indicates, should be free from accessory crystallised in- 
gredients. North Wales, Lehsten in the Thuringian Forest, &c. 
(c) PENCIL-SLATE, PINSILL \ A clay-slate of pure composition, 
or PENCIL. f soft, but withal firm; separated or 

* se P ara ^ le into pencils (the slaty clea- 
vage crossing the planes of lamina- 
tion), and used for writing on slate. 

Found in North Wales, Sonnerberg in the Thuringian Forest, 
and other slate districts. 



ARGILLACEOUS GROUP. 265 



Varieties in Composition. 



(d) WHETSLATE, WHETSTONE, HONE/ 
OILSTONE, NOVACULITE. 

WETZSCHIEFER. Germ. 

SCHISTB 8IUCEUX (NOVACULAIRE), De 

Charpentier. (Fr.) 



This is a very highly sili- 
ceous clay-slate, perfectly 
compact and homogeneous. 
Usually only indistinctly 
of slaty cleavage, and its 
fracture often conchoidal and even splintery. Used for sharpen- 
ing knives and other instruments. E. g. Wales, Devonshire, 
Katzhiitte in the Thuringian Forest. 

0) CARBONACEOUS CLAY-SLATE. ) Passes into alum-schist and 

Kon ( r SJ? ) CHER T 110 * 8011 11 - [ black chalk (Zeichnenschiefer), 

SCHISTE HOUILLER. (Fr.) ' see p. 257, ante. 

(/) ARENACEOUS CLAY-SLATE. ] Passes into argillaceous sand- 

SAXUIGER THOXSCHIEFER (GRAU- \ stone. Bv the Germans it 

WACKENSCHIETER). (Germ.) I j g frequ / ntly termed ^^ 

wacke-slate, from its occurrence in the transition or greywacke* 
formations. 

(g) MICACEOUS CLAY-SLATE. ) Differing from clay- 

<-,UMMERREICHER THoxscHUFER. (Germ.) \ mica-schist, in that the 

8CHI8TE MICACE (PAILLKTE). (Fr.) 



dently only mechanically dispersed. This variety also passes 
in Germany under the name of greywacke"-slate. 
(A) CALCAREOUS CLAY-SLATE. ) Containing numerous lenti- 

KALKKXOTIGER THONSCHIEFER (KRA- L cular or irregular nodules 

j of limestone (which fre- 

quently owe their origin to fossils) j passes over into nodular 
limestone. 

The varieties which we have already described under 
the head of argillaceous mica-schist we find repeated in 
the clay-slate, and accordingly we have : chlorite-slate, 
talc-slate, sericite-slate, ottrelite-slate, chiastolite-slate, 
nodular and spotted or mottled slate, alum-slate, and 
carbonaceous slate. 

Clay-slates are usually very distinctly stratified, although 
their slaty cleavage does not in general correspond with 
the planes of their stratification. 

Clay-slates ar not confined to one geological period of 
formation ; the genuine clay-slates, however, usually only 
occur in the older formations, viz. the transition or grey- 
wacke. In the newer formations shales are usually 
found. Nevertheless there are exceptions to this rule; 
in the Alps there occur genuine roofing slates, also com- 
mon arenaceous and micaceous clay-slates (Grauwacken- 
schiefer) belonging to the Chalk and even to the Tertiary 
periods. 



266 SEDIMENTARY ROCKS. 



Geological Varieties. 

(1) GLAEUS SLATE. \ A genuine clay-slate, in part a 

MATTERERSCHTEFEK, Heer. [ roofing-slate, occurring in Switzer- 

Scm^^iNE ( LUIS A* T ). l *> ^longing to e of tte ^ 
(Fr.) i tiary penods. 

(2) CYPRIS SLATE. ) A clay-slate with ftmefiJMe, the 

CYPRIDINERSCHIEFER. (Germ.) \ upper member of the Devonian 
SCHIKTE A CYPRIDINE. (/y-.) J formation at the Rhine and Hartz. 

(3) WISSENBACH SLATE. ] A c i ay . s i at e of the Devonian 

WlSSENBACHERSCHIEFER. (Germ.) f f , 4.1 TT 

SCHISTE DE WISSBNBACH. (Fr.) ) aUttUOUn at the Hartz. 

(4) CALCEOLA SLATE. ) A Mack and sometimes calcareous 

CALCEOLASCHIEFER. (Germ.) [ clay-slate of the Devonian forma- 
SCHISTE 1 CALCEOLES. (Fr.) ) tion at the Hartz. 

(5) GREYWACKE-SLATE. ) An arenaceous and usually mi- 

GRAUWACKEXSCHIEFER. (Germ.) \ caceous clay-slate of the transi- 
GRAUWACKE SCHISTEUSE. (Fr.) > t ion periods. 

(6) GBAPTOLITE SLATE. ^ ,4 clay-slate or sometimes a si- 

GRAPTOLITENSCHXEFER. (Germ.) I liceous slate (lydian-stone) With 
SCHISTE 1 GRAPTOLTTES. (Fr.) ) Graptolites, belonging to the Si- 
lurian formation. 



31. AKGILLACEOUS SHALE, SHALE. 

SCHIEFEETHON. (Germ.) 
AEGILE SCHISTEUSE. (Fr.) 

A laminated clay-rock ivhose fissile texture is due to its 
original stratification and not to slaty cleavage. In 
other respects, similar to clay-slate. Shale and clay- 
slate pass into each other, and many shales show a 
tendency more or less decided towards a slaty cleav- 
age. Shales are usually more recent, geologically 
speaking, than the genuine clay-slates. 



Varieties in Texture. 

(a) COMMON ARGILLACEOUS SHALE. \ Is only a softer, less firm, 
GEMEINER SCHIEFERTHON. (Germ.) I and more earthy variety of 
ARGILE SCHISTEUSE COMMUNE. (Fr.) j clay . slate w ' lih ^t its cleav- 

age, but laminated according to the plane of its original 
deposition. It is often mixed with quartz grains and with 
flakes of mica. 

(&) SCHIEFERLETTEN (of German geologists) is a modification of 
the usual argillaceous shale in which the clay is still some- 
what moist, and the rock therefore is somewhat plastic and 
greasy^ 



ARGILLACEOUS GROUP. 267 

Varieties in Composition. 

(c) BITUMINOUS SHALE. ) Of dark-brown colour, pass- 

BITUMINOSER SCHIEFERTHON. (Germ.) r ing into Brandschiefer. 
SCHISTS BITUMINEUX. (Fr.) ' 

(d) CARBONACEOUS SHALE, CARBONIFEROUS] Dark-grey to black, 

SHALE (BATT or BASS, KELVE). I from admixture of 
KOHLENSCHIEFER. (Germ.) r carbonaceous matter ; 

SCHISTE HOUIIXER. (Fr.) ) frequentlyarenaceou ; 

or micaceous. When many fossil plants occur in the rock, it is 
sometimes called in Germany Krauterschiefer. This rock es- 
pecially belongs to the Coal formation. 

(e) VARIEGATED SHALE. ] Yellow, red, violet, or green, 

BUNTER ^^ 1 ON ^^ [ according to the different degrees 
rm '') of oxidation of the iron which it 



contains. 
(/) ARENACEOUS SHALE. 1 Passing into argillaceous sand- 

SANIUGER SCHIEFERTHON. (Germ.) \ stone 

SCHMTTE 8ABLEUX. (Fr.) 

(ff) MICACEOUS SHALE. ) Corresponding with mi- 

GLIMMERREICHER SCHIEFERTHON. (Germ.) \ caceous clay-slate. 

SCHISTE MICAC6. (Fr.) J 

(A) CALCAREOUS SHALE. ) Slightly effervescing with 

MBRGELIGER SCHIEFERTHON. (Germ.) f ac id . passing into calca- 
IMARNBUX ' *** ] reous slate*" 



Geological Varieties. 

(1) FLYSCH, an arenaceous and micaceous shale, sometimes approach- 

ing the state of a clay-slate. Eocene in the Alps. 

(2) FUCOIDAL SHALE ) With remains of Fucoids. Eocene 

FUCOIDENSCHIEFER. (Germ.) \ and older in the Alns and Can>a- 

SCHI8TE X FUCOlDES. (Fr.) I tjjjjjjjg 

(3) ROETH, a term employed by the German geologists for a varie- 

gated arenaceous shale, which occurs imbedded between the 
Sluschelkalk and variegated sandstone (Thuringia) . 



* 'The colliers' and quanymen's terms for shale are bind, blue- 
bind, metal, plate, &c. ; when very fine and containing a large pro- 
portion of carbonaceous matter, the collier calls it batt or bass, the 
geologist carbonaceous (or bituminous) shale, and the coal merchant 
often slate. In Scotland the collier's term for shale appears to be 
blaes or blues, the shale being often bluish-grey ; when lumpy they 
are called lipev blaes. Black argillaceous shales or " batts " are 
called " dauks. Fekes or grey fekes seem to be sandy shales such as 
would be called rockbinds in South Staffordshire (see Williams' 
" Mineral Kingdom.") In the South of Ireland, carbonaceous shale is 
called kilve, and indurated slaty shale is termed '' pinsill " or "pencil," 
as it is often used for slate pencils.' Jukes. 



268 SEDIMENTARY KOCKS. 

(4) WERFNER SCHIEFER, a shale, usually arenaceous and micaceous, 

occurs in the Alps in strata, which there represent the varie- 
gated sandstone formation. 

(5) CARBONIFEROUS SHALE or SLATE. ] This is a geological 

KOHLENSCHIEFER (KRAUTExscHiEFEB). (Germ.) \ designation applied 

j to all shales of the 

Coal formation, whether or not they actually contain carbon 
(see ante, e). 

(6) POSIDONOMYA SHALE. ~\ A dark-coloured shale of the 

POSIDONOMYENSCHIEFER. (Germ.) I Carboniferous formation (that 
SCHISTEXPOSIDONOMYES. (FT* J of the Lias formation is a bitu- 
minous marl- slate). 

(7) WENLOCK SHALE. Silurian formation, England. 

The following relate chiefly to chemical analysis of clay- 
slates and argillaceous shales. 

References. 

O. L. Erdmann, Thonschiefer in Thiiringen, Joum. f. techn. 

Chem. 1832, vol. xiii. p. 114. 
Frick, Thonsch. in Thiir. am Harz in Westphalen, Poggend. 

Ann. 1835, vol. xxxv. p. 193. 
Pteischly Thonsch. in Bohmen, Journal f. prakt. Chemie, 1844, 

vol. xxxi. p. 45. 
Delesse, Thonsch. in den Vogesen, Ann. des Mines, 1847, [4] 

vol. xii. p. 303 ; 1853, [5] vol. iii. p. 747 j and Bullet, de la Soc. 

ge"ol., [2] vol. x. p. 562. 
Forchhammer, Thonsch. v. Christiania, Oversigt over det K. 

Danske Vidensk Silesk Forhandlinger, 1844, p. 91. Journ. 

f. prakt. Chem. 1845, vol. xxxvi. p. 394 ; and on Bornholm, 

Berzelius, Jahresber. 1844, [25] p. 405. 
Dahl, Thonsch. bei Christiania, Nyt. Mag. f. Naturv. 1848, [5] 

p. 317. 
Kjerulf, Thonsch. bei Christiania, in Christianias Silurb. 1855, 

p. 34. 
Jwanhow. Thonsch. bei Christiania, Mem. Acad. de St. Petersb. 

1859, [6] p. 325. 
Wilson, Thonsch. in Schweden, Phil. Mag. 1855, [4] p. 114 ; 

p. 417. 
K. v. Hauer, Thonsch. in Steiermark, Jahrb. d. geol. Eeichs- 

anst. 1854, pp. 362 and 869. 

J^r/ew^'&,Weriher Schiefer, Jahrb. d. geol. Reichs. 1855, p. 852. 
Sauvaqe, Ardennenschiefer, Ann. des Mines, 1845, [4] vol. vii. 

p. 420. 
List, Tannusschiefer, Ann. d. Chem. u. Pharm. 1852, vol. 

Ixxxi. pp. 192 to 260. 
Kayser, Thonsch. von Clausthal, v. L. u. Br. Jahrbuch, 1850, 

p. 682. 
Schnabel, Amelung and v. d. Mark, in den Verhandl. d. naturh. 

Ver. d. pr. Rheinlande, 1851, pp. 10, 56, and 127 j 1853, p. 

127; and 1855, p. 122. 
Rissc, Geol. Beschr. d. Gegend von Baden, 1861, p. 47. 



ARGILLACEOUS GROUP. 269 

32. CLAY and LOAM. 

THON und LEHM. (Germ.) 
ARGILE. (Fr.) 

These are earthy deposits chiefly consisting of clay, and 
when moist are more or less plastic. 

Loam or lehm is a word of German origin ; between it 
and clay there is no sharp distinction. The purest and 
therefore the most plastic varieties are called clay (also 
potter's clay or pipe-clay). They are usually white or 
greyish-blue, but sometimes yellow, red, or greenish, 
or (if containing carbon) even black. Those varieties 
which contain much fine sand and hydrated oxide of iron 
are called loam (in Germany, Lehm), and the iron usually 
gives them a yellow or brownish colour. 

Varieties in Composition. 

(a) CLAY. ) The purest varieties are white or light-bluish 

THON. (Germ.) j. grey, and are very plastic. These are called 
" ) potter's clay or pipe-clay. Those containing 
much silica or fine sand are called fire-clay ; those containing 
bitumen, bituminous clay; some are variously coloured by 
different oxides of iron, and are then termed variegated clay. 
(6) LOAM. ) Contains more or less sand, flakes of mica, and 

LEHM. (Germ.) j guc h like admixtures ; is coloured by hydrated 
oxide of iron, and is therefore less plastic than clay, almost 
earthy and yellow or brown in colour. It sometimes even con- 
tains small crystals of felspar (Glasurlehm of the Germans) ; 
or it contains particles of lime, marly loam (Mergellehm) j or 
nodules of marl (Losskindeln) ; nodules of pyrites (Kiesknollen) ; 
microscopic shells, &c. If it contains a very large proportion 
of hydrated oxide of iron, then it passes over into yellow ochre 
(Gelberde), which is used as a colouring matter, 
(c) SALIFEROUS CLAY. j A clav containing chloride of sodium, 
SALZTHON. (Germ.) L sometimes with distinct grains or crys- 
ARGILK BALiFfcRE. (fr.)J ^ of this salt ; usually occurs together 
with rock-salt. 

The following are the geological terms of certain 
clays : 

(1) LOESS, or DILUVIAL LOAM. \ Frequently somewhat calcareous 

L^L^ILUVIKN. (Fr.) J ^th marly nodules (Losskindeln). 

(2) TILE OR BRICK EARTH. A Miocene or Neogene deposit of clay 

TKOBL. (Germ.) i i n the Vienna basin. 

(3) BROWNCOAL CLAY. > Usually white. Miocene in North- 

BRAUNKOIILENTHON. (Germ.) j ern Germany. 



270 SEDIMENTARY BOOKS. 

(4) SEPTARIAN CLAY. > Containing septaria of lime, in North- 

SEPTARIENTHON. (Germ.)} ern Germany Miocene (or Eocene). 

(5) BARTON CLAY. Hampshire, Eocene. 

(6) BOGNOR CLAY. Eocene of the Hampshire basin. 
7 LONDON CLAY. Eocene in the London basin. 



(*.,} Eocene in the Paris basin. 
(9) HILS CLAY. \ In the Hils formation (Wealden) of West- 

HILSTHON. (Germ.) J phalia. 

(10) SPEETON CLAY, in the Lower Greensand formation of England. 

(11) WEALD CLAY. ) In the Wealden formation of Sussex. 

ARGILE WEALDIENNE. (Fr.) ) 

(12) ORNATEN-THON. (Germ.) With Ammonites ornatus in the Jura 

formation of Swabia. 

(13) OPALINUS-THON. (Germ.) With Ammonites opalinus in the 

Brown Jura of Swabia. 

(14) KIMERIDGE CLAY. \ In the Jura f ormat ion of England. 

ARGILE KIMMERIDIENNE. (Fr.) > 



(16) AMALTHEEN-THON. (Germ.) With Ammonites amaltheus, in the 

Lias formation of Swabia. 

(17) TURNERI-THON. (Germ.) In the Lias formation of Swabia. 

(18) MIACYTEN-THON. (Germ.) Containing Myacites, and frequently 

also remains of plants, the lowest branch of the Keuper forma- 
tion in Thuringia. 

As clay loses its plasticity when subjected to a strong 
pressure, especially if accompanied by high temperature, 
the plastic clays are chiefly confined to the recent forma- 
tions : the older clays have doubtless been converted into 
argillaceous shale, clay-slate, or claystone. There can 
be no doubt that all these rocks originally were mud 
deposits. 

Literary references on the subject of clay and loam 
appear unnecessary. 



33. CLAYSTONE and HARDENED CLAY. 

THONSTEIN, oder VERHARTETER THON. (Germ.) 

A compact and tolerably solid mass, chiefly consisting of 
clay, not slaty ; its fracture earthy ; very variously 
coloured. 

The rock designated by this name is not always an 
actual sediment, but sometimes a product of the disintegra- 
tion of felsitic rock. The nature of its origin is generally 
only to be determined by its geological position and sur- 



MARL GROUP. 271 

roundings. The sedimentary claystones are always stra- 
tified sometimes in very thin layers, white, yellowish 
grey, red-brown, greenish, or brownish, sometimes with 
variegated stripes or spotted. They sometimes contain 
nodules of pyrites, flakes of mica, impressions of plants, or 
petrified parts of plants. 

We have already said that the distinction between the 
sedimentary claystones and certain weathered felsitic 
rocks is sometimes difficult. In like manner it is fre- 
quently difficult to distinguish the former from certain 
tuff rocks, e. g. from porphyry-tuff, which indeed is very 
often called claystone, especially in England; but the 
genuine sedimentary clay rock seems to have at least as 
good a title to the name. 

MARLS. 

These are closely allied to the clays, standing between 
them and the limestones. They are in fact compounds of 
clay and carbonate of lime, and also sometimes contain 
carbonate of magnesia ; they likewise frequently contain 
fine particles of quartz, flakes of mica, oxide of iron, 
bitumen, or carbon. According to their state or texture, 
they may be divided into the slaty, the compact, and the 
earthy varieties ; according to the predominance of one or 
other of their ingredients, they may be further divided 
into the calcareous, dolomitic, arenaceous, micaceous, fer- 
ruginous, and bituminous. Of carbon they only contain 
very subordinate quantities, serving as a dark colouring 
matter. 

The original state of these rocks, like that of the clays, 
was a muddy sediment somewhat more various in its 
character than in the case of those rocks. The same 
process of pressure has consolidated them into firm, rocky, 
slaty, or sometimes bituminous masses. 

The processes of animal and vegetable life have even 
participated in the formation of some of these rocks to the 
extent of contributing their calcareous and bituminous 
ingredients. The calcareous ingredients often show traces 
with the microscope of organic remains. Marls as well 
as clays occur in the deposits of almost every geological 
period; and as to the di Terence between those of different 



272 SEDIMENTARY ROCKS. 

periods, we can only in general terms say that the older 
varieties are usually slaty or fissile, whereas in the more 
recent deposits earthy varieties more frequently occur, 
but this is by no means a rule without exception. 

34. MAKL. 

MERGEL. (Germ.) 
MARNE. (Fr.) 

A compound of clay and lime, earthy, compact, or fissile, 
usually soft; crumbles on exposure to air, effervesces 
with acid. 

Marl is a compound of clay and lime or dolomite, but 
its ingredients are blended together and cannot be dis- 
tinguished except by chemical agents. The proportion 
of lime or dolomite varies from 10 to about 50 per cent. 
Outside of these limits the rock ceases to be marl, and does 
not crumble on exposure to the air. It will then either 
be a clay or a limestone. 

The most frequent colour is grey, but marl is sometimes 
yellow, brown, red, violet, bluish, or greenish. 

Varieties in Texture. 
(a) MARL-SHALE. ] In fresh state very similar to argil- 



MERGELSCHIEFER. (Germ.) laceous shale, but crumbles on ex- 

MAKNEUX. (Fr.) 



tains much quartz, sand, mica, or bitumen. 

(b) COMPACT MARL, or MAKLSTONE. ] Without distinct fissile 

DICHTER MERGEL, VERHARTETER MERGEL, [ s l at y structure, similar to 

STEIKMERGEL, Oder MERGELSTEIN. ^^ ^ f^ fo 

MARNE COMPACTS. (Fr.) > pieces on exposure to the 

air. Admixtures of quartz and mica or bitumen similar to 
marl-shale. A modification of compact marl, separates into 
small conical concretions (cone in cone). Germ. Tuten- Merc/el. 

(c) EARTHY MARL. ) In its dry state resembles clay, but 

ERDIGER MERGEL. (Germ.) > is not plastic when wet. Its ingre- 
dients are the same as those of the other marls. 

Varieties in Composition. 

(d) CALCAREOTTS MARL. ) with much carbonate of lime in its 

KSfSSiB^P composition. 

(e) DOLOMITIC MARL. ) With dolomite, and usually also 



DOLOMITMERGEL. (Germ.) r with carbonate of lime. The dif- 
MARNE MAGXESIEK.NE. (Fr.) > f erenceg be tween (d) and (e) can 
only be determined by chemical analysis. 



MARL GROUP. 273 

(/) ARGILLACEOUS MARL. ) With little carbonate of lime or dolo- 
THOXMEKOKL. (Germ.) \ mite : forms transitions into clay, clay- 
MAIIXK AHGILEUSE. (Fr.) J 8t()ne) or ^^0^ shale. 



O) ARENACEOUS MARL. ^ 

SAM.MKHGEL. (Germ.) \ With much sand. 
MAKNE SABLEUSE. (Fr.) ) 

(A) MICACEOUS MARL. % . 

GLIMMERMERGEL. (Germ.) \ Contains mucn mica. 
MARXE MICACEE. (Fr.) ) 

(t) BITUMINOUS MARL. ) Usually in the form of shale, al- 

BiTUMiNosr.u MKIUJEL. (Germ.) j ways dark-coloured by reason 
MARXK r.m M.NK, SK. (Fr.) > of ^ bitumen> sometimes even 

black. To this belong the so-called Oelschiefer (oil-slate) and 

Kupferschiefer (cupiferous slate) of the Germans ; the latter is 

distinguished by the quantity of copper which it contains. 

(A') GLAUCONITE MARL. } With much glauconite in its compo- 

GLAUKOXITMERGEL. (Germ.) L 8 ition, and by it coloured green. The 

MAKXK GU.UCOXIEUSE. (Fr.) | ^^'^^ when examined under 

the microscope, appear mostly to proceed from the shells of 
microscopic Foraminiferae. 

(0 GYPSEOUS MARL. , A marl penetrated by stringy veins of 
*!??&. J gyP^m, or thin laminae of the same. 



Besides the above-mentioned varieties of composition, 
some marls have been named according to their geological 
position ; e. g. : 
(1) SUB-APENNINE MARL. ) 

SUBAI-KXNINKX-MEROBL. (Germ.) \ Pliocene in Upper Italy. 
NE SUBAPEXXIXE. Fr. ' 



MABNE SUBAPEXXIXE. (Fr.) 



(2) CYRENIAN MARL. ) With many Gyrenes : Miocene, in 



) 
( ^- } I 



the Mayence basin. 



(3) CHALK MARL. ) i n the Chalk formations of England 

Ki;KinKMEHQEU (Germ.) . TTVoct^linlifl. 

CRAIE MARNEUSE. (Fr.) ) and Westphalia. 

(4) PLAXER MARL. \ In the Quadersandstone formations of 

PLAXEIIMEIIOEL. (Germ.) > Saxony and Bohemia. 

(5) FOLKESTONE MARL. I j n the Gault formation of England. 

MARXE DC GAULT. (Fr.) > 

(6) SPEETON MARL, belonging to the Lower Greensand formation of 

England. 

(7) FOREST MARL. | j n t h e Lias formation of England. 

CALCAIRE MARNEUX. (Fr.) > 

(8) LIAS SLATE. ) A bituminous marl-slate of the Lias 

LIASSCHIEFER. (Germ.) I formation, sometimes called Oel- 

8CHIOTE L1A8IQUE. (Fr.) 



(9) JURENSIS MARL. ) With Ammonites jurensis, in the 

JIKEXSIS-MEROEL. (Germ.) } Lias formation of Swabia. 

(10) POSIDONOMYA SLATE. ) A dark bituminous marl-elate 

PosiDoxoMTEN-ScraEFER. (Germ.) i- of the Lias formation of Swa- 

J bia, with many Posidonomya. 
T 



274 SEDIMENTARY ROCKS. 

(11) NTJMMISMALIA MARL. \ With Terebratula mtmnwmalis, 

NUMMISMALIS-MERGEL. (Germ.) I in the Lias formation of Swabia. 

(12) BELEMNITE MAEL. ) A dark bituminous marl -slate in 

BELEMNITENSCHIEFER. (Germ.) [ the Lias formation of Swabia, 
MARNE A BELEMNITES. (Fr.) J with many ^ tefc 

(13) SPOTTED MARL, or ALGAU SLATE. \ In the formation 

FLECKENMERGEL, oder ALGAUSCHIEFER. (Germ.) ]" Q the Northern 
Alps answering to the uppermost Lias. 

(14) KETJPER MARL. ) Chiefly variegated in colour, fre- 



f7 quently withypsun, 

(15) PARTNACH SLATE, or BACTRILLIAN SLATE. ) A marl formation 

PARTNACHSCHIEFER oder BACTRILLIENSCHLEFER. L -with thick slaty 

J cleavage, which in 

the Northern Alps is found in part answering to the Keuper 
formation. 

(16) BITUMINOUS MARL-SLATE. ) Of the Zechstein forma- 

BITUMINOSER MERGELSCHTEFER. (Germ.) j tion of Thuringia. 

(17) COPPER SLATE. \ Is a bituminous marl-slate of the 

KUPFERSCHIEFER. (Germ.) j Zechstein formation of Thuringia, in 
which various sulphurous compounds of metals are contained. 
These sulphur compounds, besides their copper, contain iron, 
silver, lead, cobalt, nickel, &c. 

It will hardly be necessary to add anything respecting 
the occurrence of marl in nature, nor to refer to literature 
on the subject. 

LIMESTONE GKOTJP. 

(Limestone, Dolomite, Gypsum, Anhydrite.) 
Pure limestone is an aggregate of particles of calcspar : 
it therefore consists of carbonate of lime. Pure dolomite 
or magnesian limestone is an aggregate of particles of the 
mineral dolomite or bitter-spar : it is therefore a car- 
bonate of lime and of magnesia. Gypsum is a sulphate 
of lime combined with water ; anhydrite is gypsum with- 
out water. 

Rocks consisting of pure limestone or dolomite rarely 
occur in nature. What we chiefly find are rocks of in- 
termediate character, which we may regard as transitions 
between the two extremes ; in other words, all limestones 
are more or less magnesian, probably consisting of an 
intimate compound of the two minerals, calcspar and 
bitterspar. 

These rocks likewise usually contain other admixtures 
in small quantities ; e. g. clay, silica, oxides of iron, or 
bitumen. The presence of such minerals occasions many 



LIMESTONE GROUP. 275 

varieties in colour as well as composition ; there are also 
many modifications in texture, so that the limestones 
present us with many very dissimilar rocks. 

It is not always easy or possible without analysis to dis- 
tinguish limestone from dolomite, even if pure, still less 
to determine the various rocks of intermediate character. 
Many rocks have been long held to be limestone which 
later chemical analysis has shown to be dolomite. Never- 
theless, the distinction is important enough to be pre- 
served, although it may be difficult always to apply it.* 
We are compelled to create an arbitrary boundary by 
determining how great a percentage of magnesia should 
entitle a rock to be called a dolomite. The mineral dolo- 
mite contains about 45*7 per cent, carbonate of magnesia 
to 54-3 per cent, carbonate of lime. We may therefore 
halve the 45*7 per cent., and say that all rocks contain- 
ing more than 23 per cent, carbonate of magnesia should 
be called dolomites, and those containing less than that 
amount retain the name of limestones. Some such divi- 
sion must be agreed on for purposes of classification, 
although otherwise of little scientific value. 

The general difference between characteristic forms of 
the two rocks may be briefly stated as follows : 

LIMESTONE. DOLOMITE. 

Hardness . . 3' Hardness .... 3-5 
Spec, jrrav. . 2'6 2-8 Spec. grav. . . . . 2*8 2*9 
Crystalline-granular lime- The crystalline-granular and sac- 
stone seldom occurs except charoid varieties of dolomite occur in 
between strata of crystalline sedimentary formations, as well as 
schists. between strata of crystalline schists. 
Many beds of limestone of Sometimes these varieties pulverise 
Silurian and carboniferous age to a crystalline sand, 
are coarsely crystalline ; as are, 
also, the limestone of some coral 

(reefs and some stalagmites. 

Very often compact. Seldom quite compact. 

Frequently oolitic. Probably never oolitic. 

Lustre, when crystalline, Lustre, when crystalline, vitreous 

vitreous. to pearly. 

* The quicksilver mines of Idria are in dolomite rock, which 
adjoins and is intersected by limestone in many places; and the 
difference between the two rocks is there very important, as the ore 
is confined to the dolomite, none being ever found in the limestone. 
TRANSLATOR. 

T 2 



276 SEDIMENTARY ROCKS. 

LIMESTONE. DOLOMITE. 

Effervesces strongly with Solid portions of the rock do not 
acid. effervesce with acid. The powder 

effervesces, especially if heated. 

Its powder, when heated When its powder is heated on 
before the blowpipe on pla- platinum foil, before the blowpipe, it 
tinum foil, adheres together. tumefies and does not gelatinise. 

The circumstances under which these two rocks occur 
in nature are very similar. They both occur in a crys- 
talline-granular state, imbedded between strata of meta- 
morphic schists ; they both form strata in formations of 
various geological periods ; but in the sedimentary forma- 
tions the dolomites are frequently also found in a crys- 
talline-granular state, whereas the limestones, though 
often crystalline, are almost always compact, earthy, or 
oolitic. Deposits of genuine dolomites are never formed 
by springs, but limestones frequently. Limestones, again, 
are more frequently fossiliferous, and they are also more 
usually distinctly stratified than dolomites. 

Gypsum and anhydrite are not so extensively developed 
as limestone and dolomite; they are prevalent only in 
distinctly sedimentary formations, and are usually crystal- 
line, seldom distinctly stratified, seldom fossiliferous. They 
are often accompanied by rock-salt. In general they are 
much more free from foreign ingredients than either lime- 
stone or dolomite. 

35. LIMESTONE. 

KALKSTEIN. (Germ.') 
CALCAIRE. (.Fr.) 

A crystalline-granular, compact, earthy, or oolitic ag- 
gregate of calcspar ; effervesces strongly icith acid; 
easily scratched with the knife. 

Spec, grav 2-62-8. 

Pure limestone consists of 56 per cent, lime and 44 
per cent, carbonic acid. It seldom occurs so pure in 
nature, but is usually more or less intimately combined 
with dolomite, alumina, silica, peroxide and protoxide of 
iron, bitumen, or carbon. By these ingredients its pro- 
perties undergo alteration, and there arise distinct varie- 
ties in composition when their quantity is considerable. 
The texture of the limestone rocks is likewise various, 
and gives rise to other varieties, to many of which sepa- 



LIMESTONE GROUP. 277 

rate names attach. Many limestones consist entirely, and 
others partially, of the calcareous shells of animals ; and 
it is very possible that this is the case with several whose 
original structure is no longer apparent. There are other 
limestones which are undoubtedly the product of chemical 
precipitate of carbonate of lime from aqueous solutions ; 
and some that are the result of consolidation of calcareous 
mud proceeding from the mechanical disintegration of 
older limestones. 

In appearance, many limestones and dolomites much 
resemble some siliceous rocks, or compact felsitic rocks, 
or gypsum. But from these they may easily be distin- 
guished by the difference of their hardness, and by their 
effervescence with acids. 

Varieties in Texture. 

(a) GRANULAR LIMESTONE. ] Including marble. A granular 

KORXIGER KALKSTEIX. (Germ.) I aggregate of distinct individual 
CALCAIRE SACCHAROSE. (Fr.) f ^J^ ^^ of calcspar . 

The grains vary in size from the almost invisibly small (fine- 
grained compact varieties) to the size of a nut (coarse- 
grained). Most usually the colour is white, but sometimes 
yellowish-grey, reddish, greenish, bluish, and even black. By 
admixture of dolomite it passes into magnesian limestone 
and dolomite. Granular limestone also contains other ad- 
mixtures, especially in its crystalline state, and these are then 
porphyritically disposed, as, for instance, mica, chlorite, talc, 
hornblende, pyroxene, garnet, vesuvian, felspar, chondrodite, 
couzeranite, chiastolite, epidote, zircon, titanite, spinel, corun- 
dum, quartz, fluor-spar, apatite, magnetic iron-ore, iron pyrites, 
zinc-blende, galena, copper pyrites, anthracite, and graphite. 
The rock also contains geodes, nests, or veins, with fully 
developed crystals of calcspar, aragonite, bitter-spar (dolomite), 
asbestus, serpentine, &c. 

The following special varieties of granular limestone are 
occasioned by the occurrence of some of the above minerals in 
considerable quantity and characteristic form. 

(</) CTPOLLINO. ] A granular limestone rich in 

CIPOLLES. (Germ.) L m i ca , by which a slaty texture is 

UN " ( r.) j sometimes occasioned; goes over 

into calcareous mica-schist. Zaunhaus, near Alten- 

berg in Saxony. 

(/3) AXTHRACONITE. ] The name given by v. Moll to 

A-NTHHAKOMT, Von L certain carbonaceous black granu- 

j lar limestones, which are usually 

only found in the form of nesta, lentils, or veins in 

other rocks. To this class belongs the Lucullite of the 

ancients. 



278 SEDIMENTARY ROCKS. 

(y) OPHICALCITE. ] The name given by Brong- 

OPHICALCIT. (Germ.) I n i ar t to a compound of lime- 

o?^, Brongniart. J Bton e and serpentine j itstex- 

ture granular to compact. 

This is the Verde Antique of archaeologists. 

((^) CALCIPHYRE. j The name given by Brong- 

CALCIPHYR. (Germ.) I n i ar t to a compound of gra- 



Brongniart. 

pyroxene, or felspar, usually 
porphyritic. 

HEMITREKE. ] A granular compound of 

HEMTTBEN. (Germ.) I limestone, hornblende, and 

' 



(y), ((>), and () are probably 
always contact formations. 

() HISLOPITE. ) The name given by Samuel Haugh- 

HISLOPIT. (Germ.) ] ton to a granular limestone occur- 
ring at Takli in the East Indies. 

Granular limestone is of irregular massive structure ; it like- 
wise usually shows distinct traces of stratification, sometimes 
also a fissile texture j it most usually occurs in subordinate beds 
between strata of crystalline schists, and is frequently itself the 
product of metamorphosis from compact sedimentary deposits 
of limestone. The form of its beds is sometimes very irregular, 
they assume a swollen shape, or resemble the dykes or veins of 
igneous rocks. It would seem as if the limestone, in the pro- 
cess of transmutation, had become softer than the surrounding 
schist, and that its mass had consequently been squeezed into 
the breaches and clefts of the latter. This appearance may 
be observed at Miltitz near Meissen, and at Auerbach near 
Heidelberg. 

In England and Ireland beds of crystalline limestone occur 
variously interstratified with the compact limestones of the 
carboniferous limestone series through a thickness of from 2,000 
to 3,000 feet. 

Granular limestone is also found at the margin of those 

igneous rocks which have broken through the compact or earthy 

limestones. Such may be observed at the Kaiserstuhl in 

Breisgau, in County Antrim and Island of Rathlin, Ireland. 

(6) COMPACT LIMESTONE. ) The particles of calcspar are in- 

DICHTER KALKSTEIN. (Germ.) \ visibly small, and the mass there- 

CAI^AIKE COMPACTE. (Fr.) I 



fore to be compact> Its 

fracture is conch oidal, or splintery, or dull. Its prevailing 
colour is grey or yellowish ; it varies, however, to white, 
blue, green, red, brown, and even black. Some varieties are 
variegated, spotted, or veined, like marble. The following ac- 
cessory ingredients are usually intimately blended with the 
general mass, viz., dolomite, clay, silica, oxide of iron, bitu- 
men, or carbon. If these only occur in small quantity, they 
can hardly be recognised, but if their quantity be consider- 
able, then distinct varieties of the rock are occasioned, such as 
the folio wing: 



LIMESTONE GROUP. 279 

(rr) DOLOMITIC. 

DOLOMITISCHER DICHTER KALKSTKIN. (Germ.) 
MAGNESIEN. (Fr.) 

63) BITUMINOUS. ) Fetid limestone, swine- 

STINKSTELV, STINKKALK, (Germ.) [ stones, always dark- 
CAIX.AIRE BITUMINEUX. (Fr.) J co i ouredj and emitting 
a bituminous smell when rubbed. 

(:/) ARGILLACEOUS or MARLY LIMESTONE. ) With consider- 

MERGELKALKSTEIX. (Germ.) [ 

CAIX^RE ARGI^UX ou MARKED. (Fr.) J 
grey, and in fracture dull, almost earthy. 

(<>) FERRUGINOUS LIMESTONE. ) Very rich in hydrated 
EISENKALKOTEIN. (Germ.) I ox j(fe of iron, which im- 
CAXCAIRE FEBKUGINEUX. (Fr.) -, 

) parts a brown colour to 

the rock. 

(*) CHERTT LIMESTONE, or SILICEOUS "I Combined with si- 
LIMESTONE. I lica, and therefore 

SSSJSSfeM I harder * t ordi - 

1 nary limestone, 
Very frequently traversed by veins of chert or hornstone. 

In all the varieties of these compact limestones there occur, 
occasionally, veins, seams, nodules, or nests of calcspar, horn- 
stoie (chert), or flint. 

Jukes remarks, l Almost all large masses of limestone have 
ther Hints or siliceous concretions. These are frequently called 
cheft, as in the carboniferous limestone (see post, p. 351), where 
the lodules and layers of chert exactly resemble the flints in 
chall. Even the tertiary limestones round Paris have their 
flints the menilite of that locality being nothing but a siliceous 
concrtion (see post, p. 349), found in the calcaire St. Ouen, and 
possity other places. Pure siliceous concretions occur even in 
the freshwater limestones and gypsum beds of Montmartre. 
This invariable, or nearly invariable, accompaniment of lime- 
stone jid siliceous deposits, those siliceous parts having a 
chemial and not a mechanical formation, strengthens the hypo- 
thesis f the organic origin of both, as previously described. 
The silca diffused through the calcareous mud, of which the 
limestoie was composed, has sometimes remained so diffused 
instead -f separating as nodules or layers, producing a cherty or 
siliceouslirnestone.' 

Page ,ays, ' To the percolation of water charged with car- 
bonic aci, we owe the production of rottenstone from beds 
of siliceas limestone, the carbonated waters dissolving the 
limy porion, and leaving the light porous siliceous residuum 
which fonis the rottenstone of commerce.' 

The ccnpact limestones are usually distinctly stratified, and 
are founc associated with other sedimentary rocks of almost 
every age 
(e) EARTHY LMESTONES. ) Chalk (in part). Rough to the 

ERDIGER KLKOTEIN. (Germ.) I f ee l ; friable ; the white chalk 

CAHAIM .UYEUX. (Fr.) J ^^ fapjfa fa ^^ fr my 

body agabst which it is rubbed. In chalk the particles consist 



280 SEDIMENTARY ROCKS. 

of very minute shells of Foraminifera, Polythalamiae, &c., which 
may "be recognised under the microscope. 

These minute shells constitute a fine earthy mass, in which 
larger fossils are likewise found, as well as nodules and layers 
of flint or chert, grains of glauconite, or of sand and other mine- 
ral substances. The following sub varieties may be named: 

() WHITE CHALK. 

WEISSE KREIDE. (Germ.) 
CRAIE BLANCHE. (Fr.) 

(/3) GLAUCONITIC CHALK. 

GLAUKOxmscHE KREIDE. (Germ.) 
CRAIE GLAUCONIEUSE. (Fr.) 

(y) ARENACEOUS SANDSTONE. \ Consisting of remains of 

SANDIGER KALKSTEIN. (Germ.) L shells. These earthy and 

CALCAIRE ARENACE. {Fr.) J distiuc tly ZOO genic rocks 

are more frequent in recent than in old formations. 

We may presume that in the older formations they 

have been metamorphosed into compact limestone. 

(d) OOLITIC LIMESTONE, OOLITE, ROESTONE,^ This variety is en- 

PEASTONE, or PISOLITE. tirely composed of 

OOLTTHISCHER KALKSTEIX, OOLITH, ROGENSTEIN, f Sma ll anc [ alniOSt 

EBBSKSsmif, oder PISOLITE. (Germ.) ""(, . f "- t f 

CALCAIRE OOLITHIQUE, CALCAIRE PISOLITHIQUE. J spneneal grams, Irom 
( Fr <) the size of a millet- 

seed to that of a pea or larger. This granular texture is very 
different from the crystalline granular. The single round 
grains usually lie close together, but this is not always the 
case; they are sometimes wide apart, connected by a com- 
pact matrix indeed they are always held together by a matrix. 
The individual grains are often of compact structure, more 
usually, however, of radial texture; sometimes both radial 
and concentric in alternate coats, with a nucleus of foreign 
substance, such as a grain of sand; sometimes they are 
nothing but fossils. The geological position of these oolites 
is identical with that of the compact limestones. The genuine 
peastone is, however, an exception. It is (e. g. Carlsbad) 
evidently a formation from a spring of water holding in solution 
carbonate of lime (see p. 94), and it moreover consists of 
aragonite and not calcspar. Jukes remarks, 'Its peculiar struc- 
ture gives to oolite the character of a freestone, working easily 
in any direction, whence its value as a building stone. Bath 
stone, Portland stone, Caen stone are well-known examples of 
oolitic limestone.' 

The pea-grit of Cheltenham is a marine formation, one of 
the oolites, only the spherical nodules are somewhat irregular 
and elliptical in shape. 

(e) NODULAR LIMESTONE. ] This variety consists entirely of 

KNOTENKALKSTEIX. (Germ.) I sma ll compact nodules or irregular 
CALCAIRE XODULEUX. (Fr.) 11 . r ., -, -, -, 

' J swellings, united and bound to- 
gether by a compact limestone mass, or by a matrix of marl or 
clay-slate. Its composition, as well as its texture, there- 
fore, presents varieties : 

(a) NODULES OF LIMESTONE IN LIME-) 

STONE or MARL MATRIX. I At Partenkirchen 

KALKKXOTEX ix KALK oder MERGEL. f in Bavaria. 
(Germ.) 



LIMESTONE GROUP. 281 

(/3) KRAMEXZELSTEDT. I Nodules of lime in a matrix 

KRAMEXZELSTEIN. (Germ.) > O f clay-slate, hence the rock 

itself is somewhat slaty. These nodules sometimes 

are nothing else than indistinct fossils. Polwand, near 

Saalfeld. 

(/) SLATY LIMESTONE. ) This is, however, usually not 

SCHIEFRIGER KALKOTEIN. (Germ.) I o f genuine slaty texture or 
J cleavage, but only a thin strati- 
fication (lamination) presenting a slaty appearance ; thus, e. g., 
at Solenhofen in Bavaria, where a finely laminated limestone 
is even used for roof-slating. 
(g) POROUS LIMESTONE. ) -IT, 

POROSER KALKOTEIX. (Germ.) \ We here distinguish between 

CALCAIHE CAVEUXEUX. (Fr.) ' 

() SPONGY LIMESTONE, APHRITE.) Very extensively de- 

SCIIAUMKALK Oder MEHLBATZEX. L veloped in the Mu- 

j schelkalk formation of 
Thuringia, and 

(/5) LIMESTONE TUFF, GALCA-) A deposit from springs, 

REOUS TUFF. I usually porous by reason of 

KALKTUFF. (Germ.) \ j^s orioin as an incrustation 

TUF CALCAIRE. (Fr.) 



(A) GEODIC LIMESTONE. ] With numerous sparry ca- 

DRUSIGER KALKSTEIN. (Germ.) I ^ties of crystallised calcspar, 

j brownspar, and the like. 

(*) CELLULAR LIMESTONE, or ROUGH j With numerous angular 

LIMESTONE. I cells or holes. These latter 

ZELLEXKALK oder RAUHKALK. (Germ.) I are sometimes occasioned 

CALCAIRE CELLULEUX. (Fr.) ) ^ ^ decfty Qr ^^e^ 

of fragments enclosed in the rocks, in which case the porosity 
of the rock is only at the surface. 

(&) BRECCIA-LIMESTONE, or LIMESTONES Fragments of limestone 

BRECCIA. I cemented together by 

BUIX CIKXKALK oder KALKBREcciE ; TnttM- r limestone. The partial 

MER und RUIXEX-MAIOIOR. (Germ.) I i j n ' -t 

BRECHE CAWAIRK. (Fr.) ) weakening or decay of 

these fragments some- 
times causes a cellular tissue on the surface of the rock. 
(/) STYLOLITE LIMESTONE. ) Names given by Ger- 

STYLOLITHEXKALK und NAOELKALK. (Germ.) [ man geologists to cer- 
CAIXAIBE A STYLOLITES. (Fr.) j tftin c J t Umestones 

which show peculiar striped jointings, so-called stylolites, or 

are made up of small conical or wedge-shaped pieces. 

(m) FIBROUS LIMESTONE ] To this variety we may reckon 

FASERIGER KALKSTEIN, FASER- I the calc-sinter and aragonite- 

CAIQUE r^Sci (Fr.) I sinter, formed by the dripping of 

' water contaimng lime m solution, 

e. g. at Carlsbad in Bohemia. There also occur seams or layers 
of fibrous limestone between beds of marl, which have clearly 
some other origin. Stalactitic calc-sinter is frequently sparry 
and not fibrous, but as it is a subordinate formation we include 
it here because of its origin. 

Over and above the varieties in texture and composi- 



2S2 SEDIMENTARY ROCKS. 

tion which we have enumerated, limestone is very various 
in its geological character, and especially in the nature of 
the fossils which it contains. The geological varieties are 
not of distinct lithological character, but they never- 
theless deserve a brief enumeration, as they sometimes 
acquire local importance. They are only to be distin- 
guished with certainty by means of their fossils ; we will 
arrange them as nearly as possible according to their 
respective ages. 

Geological Varieties. 

(1) LIMESTONE TUFF, CAL- \ Usually a porous friable deposit from 

CAREOUS TUFF. I springs, and containing many remains 

KALKTUFF. (Germ.) rf rdirnta imd imriid 

TUP CALCAIRE. (Fr.) ' OI P lants ana animals. 

(2) TRAVERTINE. \ A formation in Italy similar to calc-tuff, 

TRAVERTIN. (Germ.) I <but usually more compact, hard, and 
TRAVERTIN. (Fr.) j sem i-crystalline.' See Bristow's Glossary, 

(3) CORAL EEEFS. \ 

KORALLENRIFFE. (Germ.) \ In tropical seas. 
CALCAIRE CORALLIEN. (Fr.) ) 

(4) FRESHWATER LIMESTONE. \ Containing freshwater shells. 

SUSSWASSERKALK. (Germ) < Freshwater limestones have com- 

t_/ALCAIRE D EAU DOUCK ^LA- I - i / / 

CUSTRE). (Fr.) i monly a peculiarity of aspect from 

which their origin may sometimes be suspected, even before 
examining their palseontological contents or petrological rela- 
tions. They are generally of a very smooth texture, and either 
dull white or pale grey ; their fracture only slightly conchoidal, 
rarely splintery, but often soft and earthy.' -Jukes. 

(5) STEPPE LIMESTONE. \ A very recent semi-marine brackish 

STEPPENKALK. (Germ.) J limestone deposit. In Southern Russia. 

(6) LEITHA LIMESTONE. \ A tertiary limestone in the Leitha Moun- 

LEITHAKALK. (Germ.) ) tains, with corals and marine shells. 

(7) LITORINELLA LIMESTONE. \ In the Mayence basin, con- 



LITTORINELLENKALK. (Germ.) taining numerous Paludinte. 

CALCAIRE A LITTORINELLES. (Fr.) 



(8) CERITHITJM LIMESTONE. ) j n the Mayence basin, with many 

CERITHIENKALK. (Germ.) f r> pri - f j )1 - f} 
CALCAIRE A CERITES. (Fr.) > 

(9) CALCAIRE GROSSIER (Grobkalk), sandy, and full of fossil shells. 

Eocene in the Paris basin. 

(10) NUMMTJLITIC LIMESTONE. \ Consisting almost exclusively 

NUMMULITENKALK. (Germ.) \ of Nmnmulites. Eocene; very 

CALCAIKE A NUMMULITES. (Fr.) j extensively deve loped in the 

South of Europe. 

' The nummulitic formation, with its characteristic fossils, 
plays a far more conspicuous part than any other tertiary group 
in the solid framework of the earthy crust, whether in Europe, 
Asia, or Africa. It often attains a thickness of many thousand 
feet, and extends from the Alps to the Carpathians, and is in 
full force in the North of Africa, as, for example, in Algeria 



LIMESTONE GKOUP. 283 

and Morocco. It has also been traced from Egypt, where it was 
larjjrelv quarried of old for the building of the Pyramids, into 
Asia Minor, and across Persia, by Bagdad, to the mouths of the 
Indus. It occurs not only in Cutch, but in the mountain ranges 
which separate Scinde from Persia, and which form the principal 
passes to Cabul ; and it has been followed still farther east- 
ward into India, as far as Eastern Bengal and the frontiers of 
China.' Page. 

(11) ORBITOIPAL LIMESTONE. ) 'As the nummulitic limestone 

CALCAIHE X ORBITOLITES. (Fr.) } seems characteristic of the old 
world, so the orbitoidal limestone seems characteristic of the 
new, mountain masses full 300 feet in thickness, and almost 
wholly made up of Orbitoides, occurring near Suggsville, in 
North America, and apparently in the same, or nearly the same, 
geological horizon.' Page. 

(12) MAJOLICA, a white compact limestone. 

( 13) SCAGLIA, a red limestone, in the Alps. 

(14) OSTRJSA LIMESTONE. \ ? u \\ O f Qstraa. Eocene ; occurs 

cSSS^SSi (Fr.) I to the north of Kusstein, in Tyrol. 

(15) UPPER AND LOWER CHALK. \ Nearly white. The upper and 

KKEIDEKALK, KREIDE. (Germ.) f principal branch of the Chalk 
formation in England, containing many flints. 

' Chalk flints occur as rounded nodular masses of very irre- 
gular and sometimes fantastic shape, and of all sizes, up to a foot 
in diameter. They are commonly white outside, but internally 
are of various shades of black or brown, sometimes passing into 
white. They have sometimes concentric bands of black and 
white colours internally, and exhibit markings derived from 
organic bodies, round which they have often been formed. 
Flint occurs in chalk, not only in nodules, but also in seams or 
layers, sometimes short and irregular, sometimes regular over a 
distance of several yards. These seams vary from half an inch 
to two inches in thickness, and are commonly black in colour.' 
Jukes. 

(16) HIPPURITIDEA, or HIPPTJRITE x Full of Ilippuritidea ; equiva- 

LIMESTONE. lent to the Lower Chalk for- 

SESTlSJS^CIh) J tion in Europe, Northern 

Afnca, and America. 

(17) RUDISTENKALK, oderHiEROGLYPHEN-<| Equivalent to the Lower 

KALK. (Germ.} \ Chalk formations. 

CRAIE X RUDISTES. (Fr.) 

(18) SPATANGUS LIMESTONE. ] Containing many Spatangida ; 

SPAT.\N.;KNK.\I.K. (Germ.) [ belonging to the Chalk group in 

CAIXUIRE X SPATANGUB*. (Fr.)\ ^ JJ 

(19) APTYCHUS LIMESTONE. ") Containing many Aptyclii-, there 

AITYCHKXKALK. (Germ.) I are two species of this fossil, one 
CALCAIRE X APTYCHUS. (Fr.) J ^^g^f^ t he Chalk, and the 
other to the Jura formation. 

(20) PLANER LIMESTONE. Thinly stratified, usually somewhat 

PLAKEUKALK. (Germ.) j marly, occurs with the Quadersandstein 
in Saxony. 



284 SEDIMENTARY ROCKS. 

(21) SERPTTLITE LIMESTONE. ) Full of fossil Serpulae ; oftheDeister 

SERPULTT. (Germ.) \ or Wealden tormation ot West- 

CALCAIRE A SERPULES. (Fr.) j phalia. 

(22) PORTLAND STONE AND OOLITE.) A limestone belonging to the 

PORTLAND-OOLITH. (Germ.) \ upper Jura of England, fre- 

CALCAIRE PORTLANDIEN. (Fr.) ) quently Oolitic. 

1 A well-known group of the upper Oolite as developed in 
the South of England. It consists of shelly freestones of 
variable texture underlaid by thick beds of sand, and derives its 
name from the Isle of Portland in Dorsetshire, where certain 
of the freestones have for centuries been largely quarried for 
architectural purposes. The Portland beds abound in fossil 
shells, bones of saurians, and drift coniferous wood.' 

(23) ASTARTE LIMESTONE. ] Containing many Astartida be- 

ASTARTENKALK. (Germ.) [ longing to the upper Jura forma- 
CALCAIRE 1 ASTARTES. (Fr.) j ^ Q 

(24) DICERAS LIMESTONE. ) Containing Dicers, and belonging 

(Fr, ) to the upper Jura formation. 

(25) CORAL RAG. \ Frequent in the Jura forma- 

KORALLENKALK, PoLYPENKALK, oder L tion, the upper member of 
CA^rS. ( 5ET ) ) the Middle Oolite in England. 

(26) NERINEA LIMESTONE. ) F U H O f Nerinece of the Jura for- 

NERINEENKALK. (Germ.) f ^t^ 
CALCAIRE 1 NERINEES. (Fr.) > x 

(27) AMMONITE LIMESTONE. ) F U H of Ammonites of the Jura or 

AMMONITENKALK. (Germ.) I T ia fnrnifltirm 
CALCAIRE AMMONITIFERE. (Fr.) > LMB IO^ m atlon. 

(28) JURA LIMESTONE. ) . 

JURAKALK. (Germ.) \ Usually white, yellowish, or grey. 

CALCAIRE JURASSIQUE. (Fr.) ' 

(29) OXFORD OOLITE. ) Belonging to the Jura or Oolite for- 

OXFORD-OOLITH. (Germ.) f . f -p no .l fln ^ 
OOLITHE D'OXFORD. (Fr.) > ma on 01 Jj^ngiana. 

(30) CORNBRASH. ) 

PLASSENKALK. (Germ.) f The same formation. 
CORNBRASH. (Fr.) > 

(31) BATH OOLITE. ) 

GRAND OOLITHE, OOLITHE f Ine 11K6. 
DE BATH. (Fr.) > 

(32) INFERIOR OOLITE. ) 

VII^ER KALIC. (Germ.) f I he like. 
OOLITHE INFERIEUR. (Fr.) ' 

(33) LIAS LIMESTONE. ) __ -,-,-,.,. 

LEIAS-KALK. (Germ.) \ Usually dark-coloured and bituminous. 

CALCAIRE LIASIQUE. (Fr.) ' 

(34) GRYPHITE LIMESTONE. | Containing numerous Grypha, the 

GRYPHITENKALK. (Germ.) L former designation for the Lias 
CALCAIRE A GRYPHITES. (Fr.) J limestone< 

(35) BELEMNITE LIMESTONE. } Containing numerous Belemnites, 



BELEMNITENKALK. (Germ.) and belonging to the Lias for- 

CALCAIRE A BELEMNITES. (Fr.) 



(36) DACHSTEINKALK (Germ.), a limestone of the Northern Alps, 

corresponding with the Lias formation in other parts of Europe. 

(37) KLIPPENKALK (Germ.), a limestone occurring in the Carpathians, 

its age not to be determined with certainty. 

(38) HALLSTATTER LIMESTONE. ) A limestone of the Alps correspond- 

HALLSTATTERKALK. (Germ.) > ing with the Keuper of Germany. 



LIMESTONE GROUP. . 285 

(39) MUSCHELKALK (SHELL \ The middle member of the Trias 

LIMESTONE). L j n Germany, usually grey, and very 

MUSCHELKALK. (Germ.) OY fpnaivplv <WplrTPrl in \\Wprn 

CALCAIRE CONCHYLIEX. (Fr.) ' extensively developed m w estera 
Germany. 

(40) AN' KLLKXKALK (Germ.), stratified in thin wavy layers, or with 

nodular concretions, the lower member of the Muschelkalk in 
Germany. 

(41) GUTTENSTEINER KALK (Germ.), a limestone of the Alps answer- 

ing to the Muschelkalk of Germany. 

(42) ENCRINAL or ENCRINITAL LIMESTONE. j Full of remains of 

ENCRIXITEN- oder TROCHJTEX-KALK. (Germ.) I Encrinites. an upper 

J member of the Mu- 
schelkalk formation of Germany. 

* The internal calcareous skeletons of the encrinites (in 
scattered joints and fragments) are so abundant in some Car- 
boniferous limestones as to compose the greater part of the 
mass, hence the term encrinal or encrinital limestone. The 
minuter joints of the lingers and rays are usually termed en- 
trochi or wheelstones, and these when abounding in certain 
limestones confer on them the title entrochal limestones. The 
stalk having been perforated by a canal which kept the whole 
in vital union, tne separated joints present a beadlike ap- 
pearance : hence such familiar terms as " St. Cuthbert's beads " 
and " wheelstones " for the solid pieces, and " pulley stones " and 
" screw stones " for their hollow casts in limestones.' Page. 

(43) TEREBRATULA LIMESTONE. ) Almost entirely consisting of Tere- 

TEREBRATULAKALK. (Germ.) L foatttla vulqaris. Frequent in the 
CALCAIRE 1 Ti BRATULK*. J Mu8chelka k of KorfhSn Germany. 

(44) ROESTOXK. ) A rock occurring in the sandstone of 

ROOENSTEDT. (Germ.) j Northern Germany. 

(45) MAGNESIAN LIMESTONE (DOLOMITIC). ) The term Zechstein 

ZECHSTEIXKALK. (Germ.) \ literally translated Slg- 

CALCAIRE DU ZECHOTEIN. (Fr.) ) nifies mine-stone, so 

called because it has to be mined or cut through to reach 
the copper-slate which lies immediately beneath it; usually 
dark- coloured and bituminous. The chief member of the 
Zechstein formation of Germany. 

(46) CARBONIFEROUS LIMESTONE, or MOUN-) hief member of the 

TAIN LIMESTONE. L Carboniferous > lime- 

KOHLEXKALK, oder BEROKALK. (Germ.) f stone formation in 
CALCAIRE CARBOXIFERE. (Fr.) ) England ; when it con- 

tains metal, it is called metalliferous limestone ; when it con- 
tains much hornstone or chert, it is called chert-limestone. 

(47) SCAR LIMESTONE, a lower member of the Carboniferous lime- 

stone in Westmoreland and Cumberland. 

(48) TRANSITION or GREYWACKE LIMESTONE. ) A limestone of 

G-RAUWACKENKALK, Oder UEBERGANOSKALK. (Germ.) f the transition p6- 

GIIAUWACKE CALCAIRE. (Fr.) ) jjod, usually com- 

pact, solid, and grey. 

(49) STRINGOCEPHALUS LIMESTONE. > Containing many StrinyocepJiahis 

STRINGOCKPHALENKALK. (Germ.) > Burt'mi in the Devonian forma- 
tion of Germany. 



286 SEDIMENTAEY KOCKS. 

(50) ELFEL LIMESTONE. \ Lying immediately under the pre- 

EIFLER KALK. (Germ.) } ceding. 

(51) ORTHOCERAS LIMESTONE. ] Full of remains of Orthocera- 

ORTHOCERATITENKALK. (Germ.) I tites belonging to the Silurian 
CALCAXKEAORTHOCEKES. (Fr.) ^ J formatioil) D e .^ in Scandinavia. 

(52) URKALK (aboriginal or primitive limestone) is a general name, 

formerly very frequently applied in Germany to denote all 
granular limestones, especially those associated with the crys- 
talline schists. 

Limestones, as we have already remarked, are of various 
origin. A few only are direct chemical precipitates from 
aqueous solutions; the greater part are probably the 
product of certain animals. Some have been occasioned by 
the washing together of lime mud. The crystalline lime- 
stones owe their state chiefly to a plutonic process of 
transmutation. 

As to their bedding in relation to that of other rocks, we 
have nothing to add to what has previously been stated. 

We only adduce a few leading references on the sub- 
ject of limestones. It would serve no useful purposes 
to cite all treatises respecting their local occurrence. 

{References.* 

Ehreriberg, on the Animal Origin of many Limestones, Die 
fossilen Infusorien, 1837, Mikrogeologie, and v. L. u. Br. 
Jahrb. 1861, p. 785. 

Darwin, on the Formation of Coral Limestones in his ' Coral 
Islands.' 

G. Rose, on the heteromorphic State of Carbonate of Lime in the 
Abhandl. d. k. Akad. d. Wissenschaft zu Berlin, 1856-1858. 

HaugMon, on Hislopite in the Philos. Mag. 1859, [17] p. 66. 

Deksse, on Hislopite in the Ann. des Mines, 1861, vol. xx. p. 435. 

L. Cordier gives his views on the formation of limestones in an 
article published in the Compt. rend. 1862, vol. Ixiv. p. 293. 
He takes them to be principally chemical precipitates from 
the sea, which formerly held much greater quantities of salts 
of lime and magnesia in solution than at present. 

Leymerie expounded similar views in his Elements de Mine- 
ralogie et de Geologic, 1861, p. 358. 

Chemical analyses of limestone exist in great va- 
riety ; but they are only of local importance, serving 
to decide the character of any given rock : for instance, 
whether it be a limestone or a dolomite, or whether it be 
fitted for building or other practical use. 

As to the formation of oolite, see pp. 94-5, ante. 



LIMESTONE GROUP. 287 



36. DOLOMITE, MAGNESIAN LIMESTONE. 

DOLOMIT. (Germ.) 
DOLOMIE. (Fr.) 

A granular, compact, or earthy aggregate of bitter-spar 
(dolomite), usually combined with some calcspar ; does 
not effervesce, or only slightly effervesces with acid ; is 
easily scratched with the knife. 

Spec. grav. 4 -* * . 2-82-9. 

Pure dolomite, or bitter-spar, is a mineral, which we 
have already described as such in the earlier part of this 
work; chemically it consists of 54 carbonate of lime to 
46 carbonate of magnesia. It is very seldom that the 
rock occurs in this pure state ; it usually contains a much 
larger proportion of carbonate of lime, and most probably 
in such case consists of an intimate compound of bitter- 
spar and calcspar. It usually also contains small quan- 
tities of several other substances, such as clay, silica, 
oxides of iron, bitumen, and the like. The chief differ- 
ences between limestone and dolomite, and the mode of 
distinguishing the two rocks, have been explained (p. 275, 
ante). In general terms, we may say that the dolomites 
closely resemble the limestones as regards their bedding 
and their other attributes, except that they are more 
frequently crystalline than the limestones, and sometimes 
even are entirely made up of small rhombohedrons. 

It was long supposed that all dolomites had been 
formed by process of transmutation from limestone. It 
is, however, much more probable that dolomites and 
magnesian limestones were for the most part formed by 
sedimentary deposit, in the same manner as the limestones 
proper. Many coralline structures, and probably many 
marine shells, contain some magnesia, and therefore may 
likewise yield magnesian limestones ; some dolomites 
again have very probably resulted from chemical pre- 
cipitate from aqueous solutions. Nevertheless the origin 
of many dolomites still remains very problematical, and 
it is by no means impossible that transmutations of lime- 
stone into dolomite may have taken place and may still 
take place in the interior of the earth. We know that 
magnesia plays an important part in the transmutation of 



288 SEDIMENTARY KOCKS. 



several rocks, in proof of which we need only instance 
chlorite-schist, talc-schist, serpentine, steatite, &c. The 
magnesia would appear in such cases to have penetrated 
in a state of solution into the pores of the rocks, whose 
character it has changed, displacing other substances. 
Haidinger has suggested that sulphate of magnesia might 
in very high temperature, and under great pressure, de- 
compose carbonate of lime, converting it into dolomite 
and gypsum ; and Von Morlot has in some measure 
confirmed this suggestion by. experiment. 

Dolomite, like limestone, has many varieties, most of 
which are analogous to those of limestone, and resemble 
them also in their geological relations ; we may therefore 
treat them briefly. ( See Sterry Hunt, in Report of Brit. 
Association for 1860.) 

Varieties in Texture. 

(a) GRANULAR DOLOMITE. ) Closely resembles granular lime- 

KORNIGER DOLOMIT. (Germ.) \- stones, sometimes however sac- 

DOLOMIE SACCHAROIDE. (Fr.) J c haroid, consisting of small rhom- 

bohedrons, sometimes crumbling into dolomite sand ; usually 

more porous than limestone. Frequently penetrated by geodes 

and cavities. Its accessory ingredients are similar to those 

of limestone, perhaps more abundant and multifarious. 

Granular dolomites are more frequently associated with dis- 
tinctly sedimentary rocks than are the granular limestones. 
(6) COMPACT DOLOMITE. } Difficult to distinguish from com- 

DICHTER DOLOMIT. (Germ.) L pact limestone, perhaps more rare. 
DOLOMIE COMPACTE. (Fr.) J ^ ccessory admixtures and varieties 
of composition are probably the same. 

(c) EARTHY DOLOMITE. j Usually rougher to the feel than 

ERDIGER DOLOMIT. (Germ.) I earthy limestone, probably owing 
DOLOMIE GROSSIERE. (Fr.) J to ^ m i croscopic J lv sma ll rhom _ 

bohedral crystals. If it be grey, which is sometimes the case, 
by reason of its accessory ingredients, then it is sometimes 
called dolomitic sand. 

(d) POROUS DOLOMITE. 

POROSER DOLOMIT. (Germ.) 

(e) CELLULAR DOLOMITE. ) 

ZELLIGER DOLOMIT (RAUHWACKE). (Germ.) \ Wltn angular Cavities. 
CARGNEULE. (Fr.) 
(/) BRECCIAN DOLOMITE, or \ 

DOLOMITE BRECCIA. I Corresponds with limestone breccia 

DOLOMITBRECCIE. (Germ.) | (? "81, ante). 
BRECHE DOLOMITIQUE. (Fr.)' 

(g) CONCRETIONARY DOLOMITE. I Consisting of a number of balls 

DOLOMIE CONCRETIONXEE. (Fr.) > touching each other either like 

bunches of grapes (when it is called botryoidal), or like 

musket-balls, or great piles of cannonshot. Many of these balls 

when broken open are found to have a radiated structure. But 



LIMESTONE GROUP. % 289 

they have been produced subsequently to the deposition of 
the mass, as is shown by the fact of the lines of stratification 
proceeding through them regularly. (Jukes.) 

Dolomite is seldom oolitic, slaty, fibrous, or stylolotic, or 
at all events, such varieties are much more rare than in lime- 
stone. 

The calcareous dolomite is very similar to the dolomitic 
limestone. The two may be said to meet half way. The 
argillaceous, bituminous, micaceous, siliceous, arenaceous, ferru- 
ginous, and carbonaceous varieties, correspond with the similar 
varieties of limestone. 

Three crystalline varieties of dolomite must, however, be 
mentioned. 

Varieties in Composition. 

( K) CHROMIC DOLOMITE. ) Is the name given by Breithaupt to a 
CHROM DOLOMIT. (Germ.) I compound of dolomite, chromite, and 
oxide of chromium, occurring at Nischne-Tagilk in the Ural, 
and valued as a marble on account of its beautiful green colour. 
The chromite appears in the form of delicate grains or crystals, 
the green oxide of chromium appears to form thin laminae. 
This beautiful rock also contains some iron pyrites and native 
gold, and appears to be penetrated by manifold veins of quartz. 

(t) DOLOMITE OF THE BINNEN THAL (ALPS). This dolomite occurs 
with very rich combination of various minerals. According to 
Hugard, it is somewhat phosphorescent in the dark. It con- 
tains the following minerals pyrites, quartz, much mica, or- 
thoclase, tourmaline, tremolite,chiastolite, garnet, ruby, realgar, 
orpiment, blende, antimony-glance, dufre*nite, binnite, celestine, 
barytes, and calcspar. (Compt. rend. 1858, vol. xlvi. p. 1261 ; 
v. L. u. Br. Jahrb. 1858, p. 591.) 

(A;) PREDAZZITE (from Predazzo, \ Is the name given by Petzold 

in Tyrol). I to a dolomite occurring at Pre- 

PREDAZZTT. (Germ.) f dazzo, in South Tyrol. It ad- 

J joins syenite-granite, of which 

it is a metamorphic product. It is white and crystalline- 
granular, resembling the most beautiful marble. Besides car- 
bonate of lime and magnesia, it contains some siliceous clay 
and some water. Hence Petzold called it a special mineral : 
probably it is a compound of dolomite and brucite. (v. L. u. 
Br. Jahrb. 1848, p. 583.) 

Geological Varieties. 

(1) CORALLINE DOLOMITE. ) Jura formation in England and 

KORALLEJJDOLOMIT. (Germ.) f Germany. 

DOLOMIE CORALLIENNE. (/V.) ' J 

(2) ALPINE DOLOMITE. \ Chief dolomite of the North- 

DOLOMDJ ALPINE (cARGNEULEs). (Fr.) j era Alps, corresponding with 
the lower part of the Lias formation. 

(3) KEUPER DOLOMITE. I in the Keuper of Germany. 

KEUPERDOLOMTT. (Germ.) ' 

(4) Fl 2SSS I Si~, } In the Keuper of Swabia. 

DOLOM1E ROUGE. (Fr.) ' 

U 



290 SEDIMENTARY EOCKS. 

(5) MYOPHORIA DOLOMITE. I In the lower division of the 

MYOPHORIEN-DOLOMIT. (Germ.) > Keuper formation. 

(6) MALBSTEIN or NAGELFELS (Germ.}. A dolomite of the upper 

division of the Muschelkalk, in Swabia. 

(7) WELLENDOLOMIT (wavy dolomite), belonging to the lower divi- 

sion of the Muschelkalk, in Germany. 

(8) MAGNESIAN LIMESTONE. > A dolomite limestone of the Per- 

CALCAIRE MAGNESIEN. (Fr.) } m i an formation in England. 

(9) ZECHSTEIN DOLOMITE. \ In Thuringia and 

ZECHSTEIN-DOLOMIT, RAUHWACKE. (Germ). ) Franken 



G0) D C Hr} ^ the Zechstein of Thuringia. 



Many different varieties of dolomite are known in the Car- 
boniferous system, or occur in the Cambrian, Silurian, De- 
vonian, and Permian formations. The dolomite of Derbyshire, 
Durham, and Yorkshire in the latter formation furnishes the 
well-known building-stone of which the Houses of Parliament 
are built. In the more recent formations, dolomite would 
appear to be less frequent, unless it be that many compact dolo- 
mites are still mistaken for limestones. 

Much has been written on the formation of dolomites since 
the first celebrated treatise on that subject of L. v. Buch, in 
Leonhard's Almanack, 1824. Of the various arguments in 
favour of the transmutation of limestone into dolomite, perhaps 
the most deserving attention is the hypothesis developed by 
Haidinger and v. Morlot, according to which the conversion 
was effected by means of solutions of sulphate of magnesia 
(Epsom salt), and gypsum was produced at the same time. 
In many cases this is very probable. (Haidinger's Naturw. 
Abhandl. vol. i.) To us it appears very probable that many 
dolomites have been formed by crystallisation of coral-reefs, as 
v, Eichthofen has ably proved in the case of some of the 
dolomites of Southern Tyrol. Vide MM. Seemann and Guyerdot, 
Bullet, de la Soc. geol. de France, (n. s.) vol. xix. p. 995,1862. 

GYPSUM AND ANHYDRITE. 

Gypsum is a combination of sulphate of lime with 
water. Anhydrite is sulphate of lime without water. 

Gypsum as a rock is much more frequent than anhy- 
drite at least ,we seldom find anhydrite on the surface 
of the earth a circumstance which is explained by its 
readiness to absorb water, and consequent conversion into 
gypsum. For the rest, the geological position of the two 
is very similar. 

37. GYPSUM. 

GYPS. (Germ.) 
GYPSE. (Fr.) 

An aggregate of sulphate of lime, usually crystalline, 
sometimes compact or fibrous - 3 soft, and usually white. 
Spec. grav. ...'... ',.- 2-3. 



LIMESTONE GROUP. 291 

Pure gypsum consists of 46*5 per cent, sulphuric acid, 
#2 '5 lime, and 21 water. It is so soft that it may be 
scratched with the nail, and only gives a dead sound when 
struck with the hammer. By these properties it may be 
most easily distinguished from white granular limestone, 
to which it bears great resemblance. Its texture is most 
usually fine-grained (alabaster), sometimes also porphy- 
ritic, containing large shining crystals of selenite. It 
is only rarely quite compact; in thin layers or narrow 
veins it is frequently fibrous or sparry. Its original snow- 
white colour is sometimes tinged grey by admixture of 
bitumen or clay, or red by oxide of iron. The mass 
sometimes (though rarely) contains as accessories some 
mica, talc, quartz, boracite, pyrites, copper pyrites, grey 
copper, zincblende, and sulphur. 

Moreover, in gypsum rock are sometimes found nests 
or veins of aphrite, anhydrite, rock-salt, sulphur, and 
chert. 

The weathered surfaces of gypsum (owing to its solu- 
bility in water) are usually much worn or eaten into. 

Varieties in Texture. 

(a) GRANULAR GYPSUM or ALABASTER. } Almost always white 

somewhat translucent. ' 



(6) PORPHYRITIC GYPSUM. ) With crystals of gypsum in a fine- 
POR (SJ,. 1 T IOEH GYP8 ' I g 111 ^ gJP sum matrix. 

(c) COMPACT GYPSUM. ) 5 are > usually mixed with clay or 
DICHTER GYPS. (Germ.) bitumen, which impart a grey colour 
GYPSE COMPACTK. (Fr.) ) to the rock. 

(rf) FIBROUS GYPSUM. ) Usually only in the form of thin veins 
FASERGYPS. (Germ.) \ or seams occurring in other gypsum, 
GYPSE FIBRETJX. (Fr.) ) or j n argillaceous shale or marl. 

(e) SPATHIC or SPARRY GYPSUM, or SELENITE. \ Occurs in similar 

SPATHIGER GYPS oder BLATTERGYPS. (Germ.). I manner to the 

J fibrous variety. 

(/) TRIPESTONE. \ Is a variety both of texture and com- 

GEKROSESTEIN. (Germ.) I position. It is formed of thin lavers 
PIERRE DE TRIPES. (/T.)J g pure white gvpsum) alternating 

with grev argillaceous gypsum, the whole twisted or crumpled 
to resemble a ruff, whence the German name. 

Varieties in Composition. 



ARGILLACEOUS GYPSUM. 
THONGYPS. (Germ.) 
MARXE GYPSEUSK. (Fr.) 

u 2 



\ Grey, spotted, or striped, by reason 

\ o f an admixture of clav. 
> 



292 SEDIMENTARY ROCKS. 

(A) BITUMINOUS GYPSUM. \ Difficult to distinguish, from the 
BrruMiNbsER GYPS. (Germ.) v last-named variety. 
GYPSE BITUMINEUX. (Fr.) ) 

(t) MICACEOUS GYPSUM. \ Mixed with mica or talc j analogous to 
GIJMMERGYPS. (Germ.) ! micaceous limestone ; of rare occur- 
GYPSE NIVIFOKME. (Fr.) J ^^ ^ ^ {a ^^ Q crygtalline 



schists, as (e.g.) on the south slope of the St. Gotthard. 

Gypsum is rarely distinctly stratified or fossiliferous ; 
both facts are in all probability connected with the mode of 
its original formation, pointing to a chemical rather than 
mechanical origin. It is contained in deposits of the 
most different periods, and exceptionally in the crystalline 
schist formations. It seldom forms extensive beds parallel 
to the other strata, but rather flat lenticular or irregular 
masses or accumulations in connection with anhydrite, 
rock-salt, and clay, or sometimes with dolomite. Some- 
times it even occurs in abnormal bedding between other 
sedimentary rocks. From the circumstances under which 
it is found to occur, it has been inferred that gypsum 
must be a product of the local conversion of limestone. 
Chemically, no doubt, this would be possible, if the 
requisite sulphuric acid were present, but such origin on a 
large scale is not capable of demonstration from any known 
facts. Some gypsum rocks may be actually shown to 
have been formed by deposit from aqueous solution of 
sulphate of lime ; others by the decomposition of pyrites 
in the immediate neighbourhood of calcspar ; others, 
again, by the absorption of water into anhydrite. Hai- 
dinger and Von Morlot have also shown that gypsum and 
dolomite may together be formed by the operation of 
solutions of sulphate of magnesia (Epsom salt) on lime- 
stone ; nevertheless all these different facts or theories of 
possible formation hardly suffice to account satisfactorily 
for the origin of the great masses of gypsum (frequently 
combined with rock-salt and anhydrite) which occur in 
the flotz or secondary series. The supposed origin of 
gypsum from anhydrite leaves the greater difficulty un- 
solved of the original deposit of anhydrous sulphate of 
lime. 

The exceptional nature of the bedding of gypsum rocks, 
as well as the frequent disturbances which appear in the 
adjoining strata, are best explained by the action of water 
in partially washing away the original deposit of gypsum, 



LIMESTONE GROUP. 293 

and also the rock-salt with which it is usually accompanied. 
The first consequences of such process would be to form 
great cavities ; after a time the roofs of these cavities 
would break down and cause disruption in the super- 
incumbent rocks. This is to us the most probable mode 
of accounting for the existing phenomena. Certain it is 
that these disturbances of the neighbouring strata are not 
of a nature to authorise us to infer an eruptive origin of 
the gypsum rock. 

The gypsum beds of different geological periods have 
not received different names, as they are not petrographi- 
cally to be distinguished from each other. It may never- 
theless be of interest to compare the different places of 
their occurrence in the European geological series. These 
are chiefly as follows : 

(1) In Miocene deposits, with remains of plants at Paria, in Italy 
with sulphur and rock-salt in Sicily. 

i2) In Eocene deposits, with bones of animals, in the Paris basin. 
3) In the Triassic formations of the French and Swiss Alps with 
rock-salt and cargneule (Lory, Favre, &c.) 

(4) In the Keuper of Germany, sometimes with rock-salt, but with- 

out fossils. 

(5) In the Muschelkalk of Germany, with anhydrite and rock-salt, 

without fossils. 

(6) In the Upper Variegated Sandstone of Germany and the Alps, 

with rock-salt and anhydrite, without fossils. 

(7) In the New Red Sandstone of England, with rock-salt, without 

fossils. 

(8) In the Zechstein of Germany, with rock-salt and anhydrite, 

without fossils. 

(9) In the Permian formations of Russia, with rock-salt. 

(10) In the clay-mica-schist of Herren-Grund, in Hungary (of un- 

doubted antiquity), with fahlerz and copper pyrites. 

(11) In the crystalline schists of the Alps at St. Gotthard, with mica ; 

at Bugg, in Switzerland, with mica and talc. 

References. 

Hausmann, Bemerkungen iiber Gyps und Karstenit, 1847. 
Karsten, iiber Gyps und Karstenit 'in his Archiv, 1848, vol. xxii. 
pp. 545 and 578. 

38. ANHYDRITE, MURIACITE, KARSTENITE. 

AMIYDRIT, MURIACIT, KARSTENIT. (Germ.) 
ANHYDRITE. (J?r.) 

A granular or compact aggregate of anhydrous sulphate 
of lime ; harder than gypsum ; white, grey, or blue. 
Spec, gray 2-82-9. 



294 SEDIMENTARY ROCKS. 

Pure anhydrite is white, and may easily be mistaken 
for gypsum or dolomite. It may, however, be easily dis- 
tinguished from dolomite by its not effervescing with acid 
even when pulverised and heated ; and it is much harder 
than gypsum. The colour of the grey or blue varieties 
is caused by the admixture of clay or bitumen in small 
quantities. There are scarcely any distinct varieties of 
texture. It occurs in nature under similar relations to 
gypsum, except that it is scarcely ever met with on the 
surface of the ground, because there, by the absorption of 
water, it is converted into gypsum. 

For literary references refer to those under the head of 
gypsum. 

FRAGMENTAL ROCKS. 

These rocks are composed of the fragments of older 
rocks, which have been broken up by mechanical forces, , 
and their parts deposited and reunited or cemented to- 
gether into a solid mass ; they are therefore termed frag- 
mental rocks. 

A somewhat similar origin may no doubt be ascribed to 
the argillaceous rocks, marls, and some limestones, but in 
this case the parent rocks have undergone chemical decom- 
position, as well as mechanical disintegration, and the dis- 
integrated parts have been resolved into very fine mud 
before the work of reconstruction commenced, so that the 
connection of the new rocks thus formed with those from 
which they spring is not so evident or easily traceable as 
in the fragmental rocks proper. 

SANDSTONES consist of grains of some mineral (usually 
quartz) compacted together ; CONGLOMERATES of rounded 
stones or pebbles cemented together ; BRECCIAS of angular 
fragments likewise bound, 

Uncompacted SAND, GRAVEL, SHINGLE, and HEAPS 
OF RUBBISH belong to this division of the materials 
of which the earth's crust is composed. 

TUFA rocks are conglomerates, more or less firmly 
united, of fragments thrown from volcanoes of the pre- 
sent or an earlier time. 



FRAGMEXTAL GROUP. 295 

39. SANDSTONE and GRITSTONE. 

SANDSTEIN, PSAMMIT. (Germ.) 
ORES. (Fr.) 

Small grains of some mineral, usually of quartz, are 
cemented together by some mineral substance. 

The process of the original formation of all sandstones 
has consisted jn the washing together of small grains of 
some solid mineral, usually quartz, and these were after- 
wards bound together into a solid rock by some cementing 
medium, or perhaps by simple pressure. In other words, 
these rocks were formed from sand, into which they may be 
resolved again. The grains are usually rounded off, and 
only exceptionally exhibit faces and edges of crystals. 

Quartz being the most abundant mineral of the earth, 
and at the same time very hard and difficult of decompo- 
sition, furnishes the material for the most sandstones ; 
these, however, also contain particles of felspar, flakes of 
mica, fragments of shells, and grains of glauconite. The 
binding medium of these grains usually consists of clay, 
marl, or hydrated oxide of iron ; less usually of silica, 
carbonate of lime, kaolin, talc, or asphalte. Sandstones 
often contain as accessories concretions of hydrated oxide 
of iron, frequently in the form of balls (eagle stones*) or 
irregular masses, nodules of pyrites, rounded pieces of 
amber, coal, and the like. 

As all sandstones are mechanical aqueous deposits, they 
are always stratified. They frequently are interstratified 
with other rocks in alternate beds, such, for instance, as 
clay-slate, argillaceous shale, marl, &c. They belong to 
no exclusive geological period, but are found in those of 
most various age. 

Varieties in Texture. 

(a) COMMON SANDSTONE. ) With grains about the size of a 

SANDSTEIN. (Germ.) j mustard-seed. 



* ' " Eagle stone," the ^Elites lapis of the ancients, fabled to have 
been laid in the nest of the eagle. A variety of nodular argilla- 
ceous iron-ore, having a concentric structure and occasionally so de- 
composed within as to have a loose kernel which rattles on being 
shaken. This kernel was known by the name of Callimus, and was 
supposed to be the young in the womb of the parent nodule ; hence 
the fable of the aetites bringing forth young. When there is no in- 
ternal kernel the nodule becomes a geode.' Page. 



296 SEDIMENTARY ROCKS. 

(6) COARSE-GRAINED SANDSTONE. ) 

GROBKORNIGER SANDSTEIN. (Germ.) h -Passing into conglomerate. 

GRES A GROS GRAINS. (Fr.) 

(c) FINE-GRAINED SANDSTONE. ) ~ _ , . . , 

FEINKORNIGER SANDSTE^ oder L Or fine sandstone, passing into an 

FEINSANDSTEIN. (Germ.) apparently compact state. 

GRES A GRAINS FINS. (Fr.) J 

(d) CRYSTALLISED SANDSTONE. ( With grains of quartz-crystals 

KRYSTALLSANDSTEIN. (Germ.) \ n wni ch the crystalline faces may 
GRES CRISTALLIN. (Fr.) ) be recognised. 

In all these sandstones the texture varies not only in 
respect of the size of the grains, but in respect of their 
quantity or abundance compared with that of the cement- 
ing medium. Some sandstones, owing to the predomi- 
nance of the latter, pass into rocks of a totally dif- 
ferent character, such as marl, claystone, &c. 

(e) FISSILE SANDSTONE. ^ Flagstone in part j usually owes 

SCHIEFRIGER SANDSTEtN oder L jt s texture to a plentiful ad- 
GRES^S"" ( ^ I mixture of mica. 
(/) GLOBULAR SANDSTONE. ] With ball-shaped concretions of com- 
KTTGELSANDSTEIN. (Germ.) L pac t or firm sandstone in a matrix of 
GRES NODULEUX. (Fr.) J ^ ^^ stmcture< In Transy l_ 

yania very extensively developed. 

According to differences in the nature of the cementing 
material, we have the following varieties : 

(ff) ARGILLACEOUS SANDSTONE. ) The most frequent variety. 

' 



GRES ARGILEUX. (Fr ' passes into arenaceous clay, ar- 

gillaceous shale, or clay-shale. 

(A) MARLY SANDSTONE. \ The next most frequent va- 

MERGEIJGER SANDSTEIN oder L ^ety. If the marl predomi- 

MERGELSANDSTEIN. (Germ.) , J ,-, ., 

GRES MARNEUX. (Fr.) ' nat es, then it passes into are- 

naceous marl or marl-shale. 

(t) CALCAREOUS SANDSTONE. "j With a calcareous cementing 

KALKIGER SANDSTEIN oder KALK- L medium ; somewhat rare ; 
G^fcS^KE* rT (Fr.) ) Passes into arenaceous lime- 

stone. 

(k) SILICEOUS SANDSTONE, -j With a very solid hornstone-like 
KEESELSANDSTEIN. (Germ.) \ cementino: material, in which the in- 
GR6s SILICEUX - (Fr '> } dividual grains of quartz are finely 
imbedded and are frequently not to be distinctly recognised. 
When these grains are intimately blended with the matrix, 
then this variety of sandstone passes into quartzite, quartz- 
rock, or a kind of hornstone. 

(7) FERRUGINOUS SANDSTONE. \ A sandstone with hydrated 

EISENSANDSTEIN oder EisENscHiissiGER [ oxide of iron, or peroxide 
GREs A F E N iNESn^.) J of iron, as its cementing 

material, which always 
gives the rock a red or brown colour. Sometimes it is spotted or 



FKAGMENTAL GROUP. '297 

striped from the unequal distribution of the iron (Tiger Sand- 
stein, Germ. ; Tiger sandstone, Engl}. If the hydrated oxide 
of iron should become predominant, as is sometimes the case, 
then we even find transitions into brown haematite. 
(m) KAOLIN SANDSTONE. \ With kaolin as cementing medium ; 

KAOLINSANDSTEIX. (Germ.) ) almost always white. Occurs, e. g., 
at Wissenfels in Thuringia. If sandstones of this description 
contain only quartz and kaolin, they form very fine fire-proof 
stones, and may be used for lining furnaces j e. g. Steinhaide, in 
the Thuringian Forest. 
(n) TALCOSE SANDSTONE. ) With a talcose cementing medium. 

TALKSANDSTEIN. (Germ.) | This varietv approaches in character 

GRES TAIAJUEUX. (Fr.) > io itacolumite, which, as we have 
already seen, is a kind of sandstone (vide p. 247, ante). 
(o) ASPHALTIC SANDSTONE. \ With asphalte as cementing me- 

ASPHAI.TSAM.STKIV. (Germ.) [ dium, a variety only of exceptional 

Ctete BITUMINEUX. (Fr.) J 



NOTE. It is frequently very difficult to determine the 
exact nature of the cementing medium, especially as two or 
more kinds often occur together in the same rock. 

According to differences in the nature and substance 
of which the grains themselves are composed, we have the 
following varieties : 

(;>) QUARTZ-SANDSTONE. QUARTZ-^ (The quartz-psammit of Nau- 
PSAMMIT. QUARTZ-GRIT. mann.) \Vith grains of quartz. 

QuARzsANDsrrEiN. (Germ.) I his is the most frequent of 

GIIES QUARTZEUX. (Fr.) ' all sandstones. 

(The mico-psammit 
(?) MICACEOUS SANDSTONE. MICACEOUS GRIT. \ ofNaumann) Con- 

GLIMMERSANDSTEIN. Mico-P8AM M rr, Naumann. f 

(Germ.) \ taming flakes of 

PSAMMITE (GRES MicACE), Brongniart. (Fr.) ) mica with the grains 

of quartz. 
(r) ARKOSE or FELSPATHIC SANDSTONE.) with g 1 of felspar as 



. 

ARKOSK. (Germ.) f well as quartz, combined 

ARKOSK. (Fr.) ) i n 8Om e cases with flakes 

of mica. This rock thus resembles granite in its composition, 
and is therefore sometimes called Regenerated granite. 
() GREEN SANDSTONE (GREENSAND).) Containing grains of glauco- 
GRtfxsANDSTEiN. (Germ.) I nite with uartz, imarti 



(Germ.) nite with quartz, imparting 

VKRT. (Fr.) J l 



the whole rock, sometimes even a dark-green colour. Ac- 
cording to Ehrenberg's microscopic analysis, these glauconite 
grains usually consist of the fossils of very minute Testacea. 
(0 SHELL-SANDSTONE. x Coral sandstone : the grains are fragments 

IU9 ^T DSmN ' f . f shells or coral '. the cementing mate- 
GRES COQUILLIER. (Fr.)) rial carbonate of lime. Rare. 

The difference between sandstone and gritstone is 
a vague and undeterminable one, as must necessarily 



298 SEDIMENTARY ROCKS. 

be the case where the things themselves are so various 
and capricious in composition and texture. The term 
gritstone is, perhaps, most applicable to the harder sand- 
stones, which consist most entirely of grains of quartz, 
most firmly compacted together by the most purely sili- 
ceous cement. The angularity of the particles cannot be 
taken as a character, since the rock commonly called 
4 millstone grit ' is generally composed of perfectly round 
grains, sometimes as large as peas and even larger : the 
stone then commencing to pass into a conglomerate.' 
Jukes. 

Jukes gives the following local terms for sandstone : 

Rock, used generally in South Staffordshire to denote any 
hard sandstone. 

Rotclie or Roche, generally used for a softer and more friable 
stone. 

Rubble means either loose angular gravel, or a slightly 
compacted brecciated sandstone. 

Hazel is a North of England term for a hard grit. 

Post is a similar term for any bed of firm rock, and is usually 
applied to sandstone. 

Peldon is a South Staffordshire term for a hard, smooth, 
flinty grit. 

Calliard or Galliard is a northern term for a similar rock. 

Freestone is a term in general use which is often applied to 
sandstones, but sometimes to limestones and even to granite, 
as in the counties of Dublin and Wicklow. It means any stone 
which works equally freely in any direction, or has no tendency 
to split in one direction more than another. 

Flagstone (see ante, p. 296), on the contrary, means a stone 
which splits more freely in one direction than any other, that 
direction being along the lines of the original deposition of the 
rock. These stones are ordinarily sandstones, though often 
very argillaceous, and some flagstones are perhaps rather in- 
durated clay in their beds than sandstone. 

Thin-bedded limestones may also be flagstones. 

Independently of the different petrographic varieties of 
sandstone, we have numerous geological varieties. These 
must always be determined by their bedding or by their 
fossils ; and they are frequently only local in their cha- 
racter. 

(1) THE MOST RECENT MARINE \ mich on some coasts is still 
SANDSTONE. in process O f formation. 

NEUESTER MEERESSANDSTEIN. (Germ.)) r 



FRAGMENTAL GROUP. 299 

(2) BLATTERS ANDSTEIN (Germ.), containing impressions of leaves of 

trees ; occurs in the Mayence Tertiary basin. 

(3) MOLASSE SANDSTONE. \ A sandstone of the Molasse forma- 

MOLASSESANDSTEIN. (Germ.) I tion on the northern margin of the 
MOLASSE. (Fr.) I Alpg . ugually 



(4) BROWNCOAL SANDSTONE. \ Sandstone of the Browncoal 

BRA0NKOHLEN8AXD8TE1N. (Germ.) j formation in Bohemia and 
Northern Germany. Miocene, Frequently siliceous sandstone. 

(5) BAGSHOT ^AND, in 'England. Eocene. 



(6) THANET SAND, in England. Eocene. 

(7) V ^K^ *.,} P^ Eocene, partly older. 

(8) C ^^^grS~.) } *** Eocene, partly older. 

(9) FUCOIDAL SANDSTONE. ) 

FUCOIDBNSANDOTEIN. (Germ.) \ With remams of Fucoids. 

- CfefeB 1 FUCOtDES. (Fr.) J 

(10) NUMMULITIC SANDSTONE. \ Containing remains of Num- 

NUMMUUTENSANDOTEIN. (Germ.) } m ,,)\+ oa 

GRES JfUMMULITHIQtJE. (Fr.) ) l XS ' 

(11) RALLIGSANDSTEIN (Germ.). A sandstone of Switzerland. Eocene. 

(12) TAVIGLIANAZ SANDSTONE. . T , 1-1 -p^^n, 

TAVioLiANAZ-SANDerEiN. (Germ.) f 

(13) MACIGNO. \ _ 

MACIGNO. (Germ.) I In North Italy. Eocene, or older. 
MACIGNO. (Fr.) ) 

(14) QUADER SANDSTONE. ) So called on account of its rectan- 

QUADERSANDSTEIN. (Germ.)} gular jointings. In conjunction with 
the planer limestone, with which it is associated and inter- 
stratified, it forms a part of the Chalk group in Saxony and 
Bohemia. 

(15) GREENSAND (UPPER AND LOWER). ] These constitute two di- 

GRUNSAND. (Germ.) \ visions of the cretaceous 

GRES^VERT (SUPERIEUB ET INFERIEUR). J grQup ^ England- 

(16) HILS SANDSTONE. \ The lowest member of the Chalk group 

HILSSANDOTEIN. (Qerm.) ) in Westphalia. 

(17) TASE^O^ ^^ | A 8an( istone of the Chalk period in Istria. 

(18) DEISTER SANDSTONE. i Westphalia, belonging to the Weal- 

DEISTERSANDSTEIN. (Germ.) j den formation. 
(10) HASTINGS SAND, England. Wealden formation. 

(20) PORTLAND SAND. Upper Oolite formation of England. 

(21) DOGGER (Germ.). A coarse-grained sandstone, brown, some- 

times very argillaceous. Whitby, Yorkshire. W T estphalia. 
Jura formation. 

(22) LIAS SANDSTONE AND SAND. I Usually light-yellow and fine- 

LHASSANDSTEIN. (Germ.) I grained. A lower member of 

J the Lias, at Gotha. An upper 
member of the Lias of England. 

(23) CARDINIA SANDSTONE. ) Containing many Thalassites 

THALASSTTKN-SANDSTEIN. [(Germ.)} (Cardmia). 

(24) 



(25) SCHILF SANDSTONE. I A member of the Upper Keuper in 
SCHILFSANDSTEIN. (Germ.) > Swabia. 



300 SEDIMENTARY ROCKS. 

(26) VARIEGATED SANDSTONE. ) So called on account of its being 

BUNTSANDSTEIN. (Germ.) \ frequently particoloured. It is, 
GRES BIGARRE. (Fr.) ) however," sometimes of one uniform 

colour (white, yellow, or red). It constitutes the chief mem- 
ber of the Buntsandstein formation of Germany. 

(27) VOSGES SANDSTONE. | Lower division of the Sandstone 

VOGESENSANDSTEIN. (Germ.) f formation of the Vosges Mountains. 

(rRES VOSGIEN. (/*/*.) 

(28) RED SANDSTONE OF THE ALPS] Corresponds with the Varie- 

(VERRUCANO). I gated Sandstone of Germany 

ROTHER ALPENSANDSTEIN. (Germ.) [ and the New Red Sandstone 
GRES ROUGE DES ALPES. (Fr.) J o f En?lancL 

(29) NEW RED SANDSTONE. Name applied in England to the whole 

series of strata lying between the Lias and the Permian rocks. 

(30) NEWENT SANDSTONE. A member of the Keuper series of 

Gloucestershire. 

(31) WEISS- oder GRAULIEGENDES. (Germ.} A White or Grey 

Sandstone (frequently conglomeratic), forming the lowest mem- 
ber of the Zechstein in Thuringia, and sometimes containing 
copper-ore (Sanderz). 

(32) CUPRIFEROUS SANDSTONE. \ A member of the Permian forma- 

KUPFERSANDCTEIN. (Germ.) I tion in Russia. Old Red Sand- 
GRES CUPRZFERE. (Fr.) J gtone of gout k of Irelan(L 

(33) ROTHER SANDSTEIN. (Germ.) Former designation for the Roth- 

liegende formation, containing arkose and other sandstones, 
usually of red colour. 

(34) CARBONIFEROUS SANDSTONE. \ White, brown, yellow, grey, 

KOHLENSANDSTEIN. (Germ.) I or almost black, in which case 
) it contains carbon. Frequent 
in the Carboniferous strata of old countries. 

(35) MILLSTONE GRIT. } Lowest member of the Coal 

formation sometimes. 



(36) GREYWACKE SANDSTONE. \ Usually very firm, with ar- 

GRAUWACKEN-SANDSTEIN, oder KOR- I orillaceous cementing medium. 

wJKfiSSTillS"* ^hen very fine-grained or 

; almost thick, it has been 

called grauwacke or quartzite ; sometimes it is very coarse- 
grained, even conglomeratic. If the clay medium should 
become slaty, then it goes over into greywacke-schist. It is 
frequent in Devonian formations. Delesse, however, appears 
to have understood something different in the Vosges under 
the term of greywacke, since he says that it consists almost 
entirely of albite, forming a felspathic matrix, containing 
quartz, hornblende, several kinds of mica, chlorite, and occa- 
sionally some carbonates. Ann. des Mines, vol. iii. p. 747 ; 
v. L. u. Br. Jahrb. 1856, p. 359. 

37) BAGGY POINT SANDSTONE (Page}. Upper Devonian. 
'38) DURA-DEN SANDSTONES, Fifeshire (Page), with Hdoptychn 
and Pterichthys. Upper Devonian. 

(39) DUNSE SANDSTONES, Scotland (Page). Red and white. Upper 

Devonian. 

(40) FLAGSTONES OF FORFAR, with Cephalaspis, Cheiracanthus, and 

Pt,erygotus. Lower Devonian. 



FRAGMEXTAL GROUP. 301 

(41) LTIDLOW SANDSTONE, micaceous, prey. Upper Silurian. 

(42) WENLOCK SANDSTONE, Upper Llandovery; gritty. Upper 

Silurian. 

(43) CARADOC SANDSTONE, frequently quartzite. Lower Silurian. 

(44) LLANDEILO and LINGULA FLAGS, laminated sandstone, rich in 

mica. Lower Silurian. 

(45) STJPER STONES, Shropshire j siliceous sandstones, passing into 

quartz rock. Cambrian. 

We will cite a few treatises only as to sandstone, re- 
lating to special varieties. 

References. 

Gerhard draws attention to the fact that the grains of quartz 

are angular and transparent in many sandstones. Abhandl. 

d. berl. Akad. 1810-17, p. 13. 
Schafthatctl found grains of amorphous silica in sandstone, v. 

Leonhard's Jahrb. 1846, p. 648. 
Zeuschncr, Sch<ifthautl, and v. Haver, on Carbonate of Lime 

and Magnesia as connecting Media, v. Leonhard's Jahrb. 

1843, p. 166 ; 1846, p. 665 j and Jahrb. d. geol. Reichsanst. 

vol. v. p. 880. 
Gntberlet published a treatise on the crystalline sandstones 

formed between the Vogelsgebirge and the Rho'n, in v. 

Leonhard's u. Br. Jahrb. 1811, p. 860. 
Ehrenberg, on Greensand, Berlin, 1856, in v. L. u. Br. Jahrb. 

1855, p. 469 ; and 1857, p. 91. 

Bischof considers the mica of the sandstone as a recent forma- 
tion. Geologie, vol. ii. p. 1450. 

Appendix. 

This seems the most appropriate place in which to in- 
troduce the mention of loose sand, which consists of in- 
coherent grains of quartz, or other mineral, and to a 
certain extent is a necessary preliminary state to the 
formation of all sandstone. 

SAND. 

SAND. (Germ.) 
SABLE. (Fr.) 

Usually grains of quartz, sometimes, however, of other minerals, 
e. g. felspar, ^dolomite, calcspar, mica, and the like ; without 
binding medium. 

These loose aggregates of mineral grains need no further 
description, although they may vary considerably in the size 
as well as the substance of their individual particles. A 
certain coarse sand is called grit. 

Sand sometimes derives a special importance from admixture 
of metallic grains or precious stones ; these, however, only occur 
locally, and are subordinate in quantity j thus, for instance, 



302- SEDIMENTAEY HOCKS. 

sand is found to contain grains of gold, platinum, tin-ore, mag- 
netic iron-ore, diamond, zircon, hyacinth, topaz, emerald, garnet, 
pyrope, &c. It is worthy of remark that such admixtures are 
almost unknown, except in the newest incoherent aggregates 
of sand or clay (stream beds), very seldom in solid sandstone. 
It may be, however, that solid sandstones do contain similar 
ingredients, and only that .they have been less subjected to in- 
vestigation than the loose superficial sand. Traces of gold 
have been actually found, e.g. in the Molasse sandstone of 
Switzerland, and again, some tin-ore has been discovered in a 
sandstone of Brittany. 



CONGLOMERATES. 
40. CONGLOMEKATE, PUDDINGSTONE. 



CONGLOMERAT, POUDDINGSTEIK. (Germ.) 
CONGLOMERAT, POUDIKGTJE. 



Pebbles or rounded stones of any mineral or rock firmly 
cemented together by media of various kinds. 

Conglomerates are of very various composition. Al- 
most the only restriction to the nature of their materials is 
that pebbles can only consist of a very firm substance 
capable of resisting decomposing influences. Their bind- 
ing medium usually consists of some of the most frequent 
and abundant of the earth's materials, such as clay, sand, 
quartz, or oxide of iron. The pebbles chiefly consist of 
quartz, lydian-stone, granite, gneiss, mica-schist, quartz- 
porphyry, greenstone, basalt, compact limestone, and the 
like ; much more rarely of sandstone, clay-slate, argilla- 
ceous shale, coal, and the like. 

A special geological importance attaches to conglome- 
rates, from the fact that they must in every case be more 
recent than the rocks whence their pebbles were derived. 
Thus they often serve to determine the relative age of 
individual rocks. By noting the position of the parent 
rocks, the geologist is often enabled to draw conclusions 
as to the course and direction of former watercourses. 
Again, they often present interesting phenomena pointing 
to certain special processes in their formation. For 
instance, the pebbles are sometimes broken or dislocated, 
their parts remaining imbedded close together ; or the 
pebbles are found marked with grooves and scratches ; 
or they are sometimes indented and forced one into 



FRAGMEXTAL GROUP. 303 

another (which latter case is the most difficult of expla- 
nation). There is a conglomerate at St. Loretta in the 
Leitha Mountains, of exceptional character, containing 
hollow limestone pebbles, the inside cavities of which are 
concentric with the outside surface. 

It is difficult to classify conglomerates, on account of 
their manifold variety. We can, of course, speak of more 
or less coarse textures we may also designate them ac- 
cording to the nature of their principal pebbles, or the 
character of their binding medium. Some examples will 
suffice to explain how such a mode of nomenclature might 
be adapted to individual cases. Taking the nature of the 
pebbles as the distinguishing feature, we may speak of 
quartz-conglomerate, porphyry-conglomerate, gneiss-con- 
glomerate, or miscellaneous conglomerate ; or, according 
to the character of the matrix, we may call the rock 
argillaceous, siliceous, ferruginous, &c. 

The following are conglomerates which have been 
specially named from their bedding or geological posi- 
tion : 

(1) NAGELFLUE. ) A conglomerate of the Molasse 

NAGELPLUHE. (Germ.) [ formation on the northern margin 

CONGIA>MERAT ALPIN. (Fr.). ) o f the Alps, the pebbles chiefly con- 
sisting of Alpine limestone, but partly of quartz, lydite, granite, 
gneiss, &c. 

(2) PLANERCONGLOMERAT (Germ.) in Saxony belongs to the Quader- 

sandstone, with pebbles of granite, syenite, or quartz-porphyry 
bound together by sandstone cement. 

(3) HILSCONGLOMERAT (Germ.), with limestone and ironstone peb- 

bles, and likewise many remains of shells, occurring in the 
lower division of the Hils formation of Westphalia. 

(4) VOSGES CONGLOMERATE. 1 Lower division of the variegated 

CONGLOMERAT vosoiEN. (Fr.) > sandstone of the Vosges, with 
many pebbles of quartz and lydite. 

(5) CONGLOMERATE OF THE WEISSLIEGENDE. I In Thuringia, the 

CONGIX>MERAT DBS WEI3SUEGENDEX. (Germ.), ' lowest member of 

the Zechstein formation, with numerous pebbles of quartz, 
lydite, and clay-slate. 

(6) CONGLOMERATE OF THE ROTHLIEGENDE. I In Germany, with 

CONGLOMERAT DBS ROTHUEGENDEN. .(Germ.) > pebbleS of " quartz, 

lydite, granite, gneiss, mica-schist, and quartz-porphyry, and 
a cementing medium of ferruginous sand. 

(7) GREY CONGLOMERATE. 1 Lowest member of the Rothlie- 

GRAUES CONGLOMERAT. (Germ.) > gende, in Saxony. 

(8) CONGLOMERATE OF HAINICHEN. I In Saxony, answering to 

CONGLOMERAT VON HAINICHEN. (Germ.) > the Carboniferous Lime- 
stone formation j containing clay-slate, mica-schist, gneiss, 



304 SEDIMENTARY ROCKS. 

granulite, granite, and greenstone j binding medium arenaceous 
and of brown colour. 

(9) GRETWACKE CONGLOMERATE. j At the Hartz, in Thuringia, 
GRAUWACKEN-CONGLOMERAT. (Germ.) \ in Bohemia, and other places, 

^ partly Devonian, partly Si- 

lurian, with pebbles of quartz, lydite, clay-slate, granite, &c. 
Binding medium argillaceous, or arenaceous, and of grey colour. 

We should state that there are some so-called pudding- 
stones which have altogether the appearance of conglo- 
merates, but, in fact, are not such, as they do not consist 
of pebbles cemented together, but they contain rounded 
concretions of some siliceous or calcareous substance. 

We shall confine our references to some treatises con- 
taining mention of special phenomena. 

References. 
Haidinger, on the Lauretta Conglomerate, in Ber. d. k. k. 

Akad. d. Wissensch. zu Wien, 1856, July 15. 
Lartet, on Pebbles showing Indentations, in v. L. u. Br. Jahrb. 

1836, p. 196. 

Blum, on the same, ibid. 1840, p. 525. 
Daithree, on the same, in Compt. rend. vol. xliv. p. 823. 
Cotta, on the same, Geol. Fragen, 1858, p. 204, and on Ver- 

worfene Geschiebe in the same account, p. 212. 
Wiirtetiberger, on the same subject, in v. L. u. Br. Jahrb. 1859, 

p. 153. 

Deicke, on the same subject, ibid. 1860, p. 219. 
GttrU, on the same subject, ibid. 1861, p. 225. 

Appendix. 
BOULDERS and PEBBLES. 

GESCHIEBE und GEROLLE. (Germ.) 

These may consist of very various materials ; and when united by a 
cementing medium, they form a conglomerate rock. 

Erratic Slocks and Boulders are of especial geological im- 
portance ; they are sometimes only partially rounded, and 
they are dispersed over the earth's surface, far from their 
parent rocks. 

They consist of very different kinds of rock, and have for the 
most part been transported to their present position by means 
of glaciers or of drift-ice. 

41. BRECCIA. 

BRECCIE. (Germ.) 

BRECHE, BRECCIOLA, Brongniart. (Fr.) 

A rock composed of angular fragments of minerals or 
solid rocks cemented or bound together by some matrix 
or binding medium. [BKECCIOLA when the frag- 
ments are small.] 



FRAGMEXTAL GROUP. 305 

Breccias, like conglomerates, may consist of the most 
various substances, both in their fragmental ingredients 
and their connecting medium, whence a similar richness 
in the number of varieties, which are too numerous and 
manifold to admit of classification. They must in each 
case be named according to the character of their in- 
gredients thus, quartz-breccia, gneiss-breccia, limestone- 
breccia, &c. or according to the nature of their matrix, 
as in the case of conglomerates. 

Breccias are geologically important, because in every 
case the fragmental parts must be of greater age than 
that of the rock itself; also because they indicate violent 
disruption of the rocks in their immediate neighbourhood, 
and from the circumstance that very angular fragments 
can never have travelled very far from the place of their 
original bedding. 

The following kinds of breccia are noteworthy on geo- 
logical grounds. 

Geological Varieties. 

(1) FRICTION BRECCIAS. ] These are breccias formed 

REIBUNOSBRECCIEN. (Germ.) I at the maroin of eruptive 

BKfcCHES DK FIU,N (DK FROTTEMHNT). ^ . ^ Jg ftt t he time pf 

J their eruption ; the matrix 

of the breccia consisting of the substance of the igneous rock, 
and the enclosed fragments being pieces of the rocks broken 
through. These breccias are very frequently found at the 
margin of porphyries, greenstones, basalts, trachytes, &c., and 
1 may be designated accordingly. 

Simler has given the name of Metamixite to these contact 
formations. (Ueber Petrogenese, 1862.) 

(2) QUARTZ-BRECCIA. \ Consisting of fragments of quartz 

QUARZBROCKENFBLS. (Germ.) \ bound together by quartz or by 
BRfccHE 8IUCEIT8B. </v.) f f erru ginous quartz. It very fre- 
quently occurs as the filling up of wide gaps or clefts in 
the crystalline schists, e.g. at Schwarzenfels in the Erzgebirge. 

(3) BONE BRECCIA. ] A breccia whose fragmental por- 

KNOCHKNBRECCIE. (Germ.) L tions chiefly consist of fossil bones. 

BHfeCHE 1 OSSKMKNTS. (Fr.) j frequently found in clefts ^ cft . 

vities of limestones, and, as it would appear, always of very 
recent origin. 

(4) HASELGEBIRGE (Germ.) is the name griven to certain breccia- 

like rocks occurring in connection with the rock-salt forma- 
tions of the Northern Alps. They consist of clay as matrix, 
and contain very various fragments of the neighbouring rocks. 
They have probably arisen from the breaking in of the roof 
of cavities caused by partial washing away of the rock-salt. 
X 



306 SEDIMENTARY KOCKS. 

TOPAZ ROCK. } This rock may be treated as a breccia, 

TOPASFELS.' (Germ.) I and is therefore placed here. We 

TOPAZOLITHE, TOPAZOGEME, f s } 1& \\ a i 80 no tice it again as a sepa- 

J rate rock (page 324, post). 
Cotta, on Breccia formation, in Geolog. Fragen, 1858, p. 186. 

Appendix. 

ACCUMULATIONS OK HEAPS OF LOOSE FKAGMENTS OF STONES OR 
RUBBISH. 

These may be naturally or artificially formed, e.g. naturally 
by the fall of a rock or mountain, or artificially by the l tip- 
ping ' of stones at the mouth of a mine or elsewhere. 

42. TUFA or TUFF. 

TUFFBLLDUNGEN. (Germ.) 
TUF. (Fr.) 

Accumulations of lapilli, fragments, ash, or other sub- 
stances, ejected from volcanoes, and more or less firmly 
compacted together. 

We can hardly, within reasonable limits, give a more 
definite description of these rocks, on account of their 
great variety both of state and composition. They may 
be best understood by a description of the mode of their 
origin ; volcanoes during their eruptions cast out masses 
or lumps of lava, usually scoriaceous so-called ( bombs ' 
which are for the most part rounded, and vary in size 
from the size of a man's fist to that of a human head and 
larger ; but besides these bombs, volcanoes also emit what 
is termed ' volcanic sand,' and even dust-like particles of 
lava or ( volcanic ash,' often accompanied by non- volcanic 
fragments which have been torn away from the sides of 
the crater. 

In still weather all such products fall on the slopes, or 
in the immediate neighbourhood of the volcano ; but in 
storms of wind they are often borne to a considerable dis- 
tance, and so become separated according to their size and 
weight. If the volcano be in the neighbourhood of the 
sea, or of a freshwater lake, then they often fall into 
these. 

They are likewise frequently washed down by floods 
of rain from the steeper slopes of the volcano, and are so 
accumulated in one or more separate localities. By such 
means they cover the land with a loose stratum, or with 
the assistance of water they become more or less regularly 



FRAGMENTAL GROUP. 307 

stratified, form deposits of various thickness ; and some- 
times trunks of trees or other substances become imbedded 
with them. Again, if these volcanic products are de- 
posited in considerable quantity, either in the sea or 
freshwater basins, then they envelope such remains of 
coral, shells, fishes, and the like, as may happen to come 
in their way, these latter being in such case converted 
into fossils. 

Such is the origin of volcanic tufa, which may therefore 
either be a land formation, or a freshwater, or marine 
formation. At some very lofty volcanoes, especially some 
near Quito, there occur streams of mud, which are oc- 
casioned by the rapid melting of the mountain snow or 
the bursting of some internal reservoir of water. The 
violent rush of water carries with it all loose materials 
with which it comes into contact, converting them into 
mud, which is deposited where the mountain slopes are 
most gradual. The mass thus formed is called Moja. It 
is, however, nothing but a kind of volcanic tufa. 

Tufas sometimes contain fragments of various kinds, 
large and small, angular and rounded, confusedly mingled 
together ; sometimes the fragments have become sorted 
according to size and weight, so that we find some tufas 
consisting entirely of fine dust resembling claystone ; 
others of small grains resembling sandstone ; and others, 
again, of only coarse fragments resembling conglomerate. 

It would be impossible to distinguish and arrange the 
manifold varieties of tufa systematically ; we can only in 
some measure indicate the local designations for particular 
varieties, commencing with those belonging to active 
volcanoes, then instancing those associated with the older 
volcanoes, or even, as sometimes happens, with plutonic 
igneous rocks. A genuine plutonic, i.e. subterranean, 
formation of tufa, is not to be imagined as possible. 
Therefore, as we nevertheless sometimes find tufas con- 
nected with and belonging to plutonic rocks, for instance 
with greenstones and quartz-porphyries, we must assume 
that these greenstones and quartz-porphyries formerly 
had an upper volcanic portion to which the tuff formations 
properly belonged, but which has since been destroyed 
and washed away, whilst a part of the tufas have been 
preserved, being perhaps protected by other deposits. 

x 2 



308 SEDIMENTARY ROCKS. 

We have no tufa formations belonging to the granites, 
because they never reached the surface in their melted 
state, and tufas and breccias are the result of eruptions 
which have taken place at the surface of the earth, or 
beneath the waters of shallow seas. 

(A) VOLCANIC TUFAS, BASALTIC AND TRACHYTIC. 

The materials of which they consist are slags, lapilli, ash, 
fragments of pumice, or lava mixed with other substances. 
Their structures are rough, earthy to compact, arenaceous, 
conglomeritic, or breccian. 

(a) PEPERINO. ) Grey wackenitic matrix, enclosing laminae 

PEPERIN. (Germ.} j o f black mica and grains or crystals of 

augite, leucite, and magnetic iron-ore; 

sometimes with angular fragments of basalt, leucite rock, 

limestone, and the like. In the Albanian Mountains it occurs 

in extensive beds of reat thickness. 



BASALT-TUFA, and BASALT-CON- 
GLOMERATE, or BRECCIA. 

BASALT-TUFF und BASALT-CONGLOMERAT 
oder BRECCIE. (Germ.) 

TUF BASALTIQUE, CONGLOMERAT BASAL- 



Fragments of basalt of 
very various sizes, joined 
together by pulverised 

particles of basalt or by 

TIQUE. ~(Fr.) clay, or some other de- 

composed rocky matter. This kind of tufa often likewise 
contains fragments or pebbles of other rocks, pieces of augite, 
hornblende, olivine, mica, and magnetic iron-ore, grains of 
glauconite, &c. It is occasionally penetrated by nests and veins 
of calcspar, aragonite, or sparry iron-ore. It frequently con- 
tains fossils. 

(c) PALAGONITE-TUFA. j This is the name given by Sartorius 

pALAGONm-uFF. (Germ.) f v . Waltershausen to a variety of basalt 
tufa, first observed by him near Pala- 

gonia in Sicily, It is probably the product of transmutation 
from ordinary basalt tufa, taken place under water. The prin- 
cipal mass of this rock consists of a peculiar mineral formation 
termed palagonite, which shapes itself into compact masses, 
or into aggregates of small grains ; and it encloses fresh pieces 
of basalt, dolerite, or basaltic amygdaloid. Palagonite itself is 
amorphous, resembling pitch, with a yellow to blackish-brown 
colour, vitreous to greasy lustre, conchoidal or splintery frac- 
ture. H. 4-5. Spec. grav. 2-4 2-6. It is a hydrous silicate 
of iron, alumina, lime, and magnesia, with little potash or soda. 

(d) PUZZULANA. 1 A loosely coherent deposit of volcanic sand, 

PUZZULAN. (Germ.) \ ve ry useful in the construction of hydraulic 
POUZZOLANE. (Fr.) J mo rtars 

(<?) TRACHYTE-TUFA, TRACHYTE-CON- -j Fragments or pebbles of 

GLOMERATE, TRACHYTE-BRECCIA. trachyte are more or less 

TRACHYTTUFF, TRACHYT-BRECCIE und h firmly cemented together 

CONGLOMERAT. (Germ.) "K -fi l i 'A 

CHYTIQUE. (Fr.) tides of the same ma- 

terial. Or the matrix oc- 
curs alone as a compact fine earth mass of a white, yellow, or 
even green colour. Sometimes it contains pieces of sanidine 



FRAGMENTAL GROUP. 309 

hornblende, or magnetic iron-ore in a better state of preserva- 
tion. In clefts and fissures of the tuft' an opal-like stone has 
found itself at Kaschau in Hungary; for instance, precious 
opal. Here and there it contains impressions of plants and 
other fossils. 

(/) PUMICEOTTS TUFA, PUMICEOUS SAND \ "White, yellow, or grey; 
and CONGLOMERATE. f its texture earthy to 

BIMSTEINTUFF, BiMSTEiN-SAND und CoNOLo- T compact, very rough 

tptte feel. It con- 
sists of an aggregate 
of pulverised particles of pumice-stone, frequently enclosing 
fragments of the same or of trachyte. As accessory ingredients, 
it also contains laminae of mica, crystals of felspar, grains of 
magnetic iron-ore, less frequently quartz and garnet. The fine 
pumiceous tufa has sometimes formed itself into small con- 
centric globules (pisolites), as happens at the present day when 
rain occurs during a volcanic shower of ash. 

(g) TRASS (Rhine), PAUSILIPPO TUFA\ Are only local varieties 

(Sicily), TOSCA (TenerifFe). I of pumiceous tufa which 

TRASS (DucK&TEiN), PAUSILIPFTUFF, TOSCA. Y sometimes contain car- 

I*J?TOTimP40Bum (Fr.) ) bonised trunks of trees 

and other organic re- 
mains, and usually are well adapted to the construction of 
hydraulic mortars. Much of this pumiceous tufa seems to be 
the product of volcanic mud-streams, and therefore to answer 
to the moja of South America. 
(h) ALUM-STONE, ALUM ROCK (Tolfa). } Is the name given to 

ALAUNSTEIN, ALAUNFELS, TOLFA. (Germ.) f a certain argilo-tra- 

' chytic tufa, containing 

alum, occurring at Bereghsacz, in Hungary, and at La Tolfa, 
in Italy, &c. But much of what has received this name is 
probably only decomposed trachytic rock, and therefore not a 
genuine tufa. 

(i) PHONOLITE-TUFA, and CON-X Fragments or pebbles of pho- 

GLOMERATE. nolite are united together by 

PHONOUTTUFF und CONGLOMERAT. L a n aggregate compound of 

TuF^^JoijTHiQUB, CONGLOMERAT hy particles, and of earthy 

PHONOLITHIQUE. (fr.) > to compact texture, sometimes 

containing sanidine, hornblende, augite, &c. It is found, e.g., 

in Hogau and at the southern foot of the Erzgebirge. 

(B) TUFF FORMATIONS OF PLUTONIC ROCKS. 

(&) PORPHYRY-TUFF, or FELSITE-TUFF \ Sometimes called clay- 
(FELSPATHIC ASH), Jukes. [ stone; a compact ag- 

PORPHYRTUFF oder FELSTITUFF. (Germ.) [ cn-egate of felsitic parts, 

TUF PORPHYRIQUE OU FEUSPATHIQUE. (Fr.) J ^^^ deC ompOSed, 

fracture earthy, often variegated in colour, seldom distinctly 
stratified, but sometimes containing fossil plants, especially 
trunks of trees. At Chemnitz, in Saxony, where this tufa occurs 
as the lowest member of the Rothliegende, it is supposed to 
belong to the quartz-porphyries of that district- It is, how- 
ever, very diificult to distinguish these rocks in themselves 
from ordinary claystones, or Jrom certain products of decom- 
position of compact or porphyritic felsitic rocks. 



310 SEDIMENTARY ROCKS. 

Porphyry-tuff sometimes encloses fragments and pebbles of 
quartz-porphyry, and thereby passes over into a kind of por- 
phyry-breccia or conglomerate. At Fidha, in Saxony, there 
occurs a porphyry-breccia of this description, the matrix con- 
sisting of crystalline particles of felspar. 

(T) GREENSTONE-TUFF, and GREENSTONE-CONGLO-] A compact ag- 

MERATE (GREENSTONE-ASH). ( gregate of pul- 

GRUNSTEINTUFF und GRUNSTEINCONGLOMERAT. (Germ.) [ verised or sand- 

TUF DIOBITIQUE et CONGLOMERAT DIORITIQUE. (Fr.) J -i-i ,- -i P 

greenstone j fracture earthy ; colour grey or brownish-green, 
sometimes enclosing fragments or pebbles of greenstone, and 
frequently organic remains. 

At Planschwitz, in Saxony, greenstone-tufa is imbedded 
between strata of greywacke slate, and contains many fossils of 
the Devonian formation. Probably much of what in Nassau 
has been called schalstein belongs to greenstone-tufa. On 
account of the indistinct character attached to the name schal- 
stein, we have preferred to treat it separately. 

In Southern Tyrol, in theFassa district, Von Richthofen 
has lately made distinctions between eruptive tufas, sedi- 
mentary tuffs, and regenerated tuffs, but they all belong 
to augite rocks, and take their geological rank amongst 
the deposits of more recent Trias formations. 

References. 

Natimann, on Porphyry-tufa, in the Erlauter. z. geogn. Karte 

v. Sachsen, 1838, No. 2, p. 434 
Gruner, Porphyry-tufa with Mica Crystals in the Dep. of the 

Loire, Ann. des Mines, 1841, [3] vol. xix. pp. 98 and 122. 
Beudant, Voyage min. et geol. en Hong-rie, vol. ii. p. 416. 
v. Oeynhausen, on Trass, in the Erlauter. z. geogn. Karte des 

Laachner Sees, 1847. 

Brongniart has given the name of Brecciole to certain basalt- 
tufas of an arenaceous texture, in the Mem. sur les terr. des 

sedim. sup. du Vincentin. Paris, 1823. 
Sartorim v. Wattershamen, on Palagonittuff : Die submarinen 

Ausbr. des Val di Noto, 1846, p. . 34 ; Skizze von Island, 

1847, p. 76; Vulk. Gest. in Sicilien und Island, 1853, pp. 

179 and 215. 
Danvin, Palagonittuff on Chatham Island, in Geol. obs. on the 

vole, islands, 1844, p. 98. 
SandbergeT) Palagonittuff at Limburg in Nassau, in Geol. Verh. 

d. Herzgoth. Nassau, 1847, p. 81. 
Girard, Palagouittuff near Montpellier, in v. L. u. Br. Jahrb. 

1853, p. 568. 

v. Richthofen, Geogn. Beschr. v. Siid-Tyrol, 1861. 
W. Evas, Felsittutf von Chemnitz Analyse, v. Leonh. u. Br. 

Jahrb. 1861, p. 643. 
Mitscherlich iiber den Alaunstein, Zeitschr. der geol. Ges. 1862, 

p. 253. 



FKAGMENTAL GKOUP. 31 L 

Appendix. 

Some part at least of what has been called schalstein belongs 
to the tufa formations ; we therefore propose here to treat of all 
the rocks to which this name has been applied, and we shall 
subjoin a few observations on the so-called laterite. 

43. SCHALSTEIN. 

SCHALSTEIN. (Germ.} 

So many rocks have been described under this name, 
that we can only say in general that by it is understood a 
laminated rock interspersed with small particles of calc- 
spar. "We must distinguish them according to their 
localities and the authors who have described them. 

(A) SCHALSTEIN, or BLATTERSTEIN-SHALE. ) In Nassau. This 

SCHALSTTEIN oder BLATTERSTEINSCHIEFER. (Germ.) } rock was certainly 
first to receive the name, but it varies greatly in its character. 
The base or matrix appears here to be a very fine somewhat 
laminated greenstone-tufa, which contains calcspar in grains or 
thin layers of green, grey, or variegated spotted colour. In 
some places, however, this rock partakes of the character of 
breccia, or is porphyritic by reason of crystals of labradorite, 
or it is amygdaloidal, or is even penetrated by clay-slate and 
chlorite-schist. In the Rhenish grauwacke district it usually 
occurs in company with greenstone (diabase) a circumstance 
which confirms its origin as a tufa formation. 

Sandberger distinguishes the following varieties of 
schalstein in Nassau: 

) NORMAL SCHALSTEIN. 
CALCAREOUS SCHALSTEIN, with much calcspar. 
SCHALSTEIN-BRECCIA, with calcspar as the cementing medium. 

SCHALSTEIN-CONGLOMERATE. 
e) SCHALSTEIN-AMYGDALOID. 

(/) PORPHYRITIC SCHALSTEIN, with crystals of labradorite. 

These are therefore varieties consisting of what under 
other circumstances we should perhaps consider quite 
dissimilar rocks, and which here are only classed together 
because of their occurring together or under similar cir- 
cumstances in the Devonian formation. 

(B) SCHALSTEIN, or CALC-TRAP, which is a somewhat slaty diabase 

or aphanite, containing grains of calcspar, and therefore may 
be classed among those greenstones (see pp. 148, 159). 

(C) SCHALSTEIN OF ZELLE, NEAR NOSSEN. ) Is only a variety of 

SCHALSTKIN VON ZELLE BET NOSSEN, oder ScHAi> I clay-slate containing 1 

HTEINAHNLICHBK THON8CHIEFEB. (Germ.) j 

loids of calcareous spar. 



312 SEDIMENTARY EOCKS. 

The name of schalstein has been used, or abused, for 
many other kinds of rock, and hence we find a tolerably 
rich literature on the subject. 

References. 

Stift, in v. Leonhard's Zeitschr. f. Min. 1825, vol. i. pp. 147 and 

*236 ; also in Geogn. Beschr. d. Herzogth. Nassau, 1831, 

p. 468. 

Oppermann, Dissert, iiber den Schalstein und Kalktrapp, 1836. 
Dollfus and Neubauer, Analyses of Schalstein in the Journ. f. 

Prakt. Chemie, 1855, vol/lxv. p. 199. 
Eglinger, Analyses, in the Jahrbuch des Ver. f. Naturk. in 

Nassau, 1856, No. 11, p. 205. 
Murchism and Sandberger, Transact, of the Geol. Soc., second 

series, vol. vi. p. 249. 
v. Dechen, in Nb'ggerath's Rheinland Westphalen, 1822, vol. ii. 

p. 71 5 and in Archiv f. Miner. Geogn. &c., vol. xix. p. 516. 
Hausmann, on the Formation of the Harz Mountains, 1842, 

p. 23. 
Sandberger, Ubers. der geol. Verh. des Herzogth. Nassau, 

1847, p. 33. 

Gumprecht, in v. L. u. Br. Jahrb. 1842, p. 825. 
Naumann, Erlauter. d. geogn. Karte v. Sachsen, 1836, No. 1, 

p. 60. 

Appendix. 

We shall here append a rock of somewhat doubtful 
character. 

LATEEITB. This is the name given by English geologists to 
certain rocks of East India, which in part are red traps, very 
much resembling brick, but others are the products of the 
decomposition of crystalline schists. Upon such uncertain 
data, of course, no definite character can be established for a 
rock. 

References. 

GumprecMs Zeitschr. f. Erdkunde, vol. v. p. 160. 
According to v. Richthofen, the laterite of Ceylon is decom- 
posed calcareous gneiss : v. Leonhard's Jahrb. 1862, p. 739. 



313 



CHAPTER IV. 

ROCKS OF SPECIAL CHARACTER OR BEDDING. 

WE propose under this general head to gather together 
several formations of very various character, but subor- 
dinate extent in point of comparative bulk hardly im- 
portant enough to be considered altogether essential 
ingredients of the earth's crust. Several of the rocks we 
have classed under previous heads are likewise compara- 
tively insignificant in point of their extent, but they form 
part of larger connected groups, and so enter into the 
family of the great rock formations of the globe. In this 
chapter we have to deal with more separate and discon- 
nected formations, frequently of local character only, and 
which we rather force into groups for the sake of conve- 
nience than in conformity with the nature of their origin, 
which is very various and in many cases doubtful. Some 
are of igneous, some of sedimentary or metamorphic 
origin, but others, in their bedding and composition, differ 
so much from the greater part of the rocks of each of 
those three classes, that we are compelled to regard them, 
for the present at least, as problematical formations, al- 
though we may account for several by supposing a con- 
currence of extraordinary and exceptional circumstances 
at their first origin or during their mutations. 

We have not, therefore, attempted to classify these 
special rocks according to origin ; but have arranged 
them somewhat arbitrarily in groups in the following 
order : 

1. Serpentine rocks. 

2. Garnet rocks. 

3. Greisen and schorl rocks. 

4. Coal and carbonaceous rocks. 

5. Ironstone rocks. 

6. Various minerals as rocks. 



314 MISCELLANEOUS DIVISION. 

SERPENTINE GROUP. 

These are rocks, probably, of very various original 
character, but which have all undergone the same special 
transmutation. This process has not been one of increase 
of crystallisation, nor of actual decomposition : it seems to 
have simply consisted in the absorption of magnesia, just 
as we know has happened in the case of many and various 
minerals. These have been converted from their original 
state into serpentine, steatite, or other magnesian com- 
pounds, and are pseudomorphs retaining the form of their 
original crystallisation. 

44. SERPENTINE, OPHIOLITE. 

SERPENTIN, OPHIOLITH. (Germ.} 
SERPENTINE. (Fr.) 

A compact rock } dull in fresh fracture, soft, with greasy 
feel, usually dark-green or brown. 
Spec, grav ; '''' .' . 2-5 2-7. 

It may be doubted whether serpentine exists as an 
original and independent mineral ; for the crystals with 
amorphous fracture, which some mineralogists call ser- 
pentine, according to others are nothing more than 
pseudomorphs of chrysolite or some other mineral. If, 
however, the existence of serpentine as an independent 
mineral were established, the question still remains 
whether the rock which we term serpentine is to be re- 
garded as consisting of such mineral, because, although 
its composition is similar, in many cases it may be dis- 
tinctly shown that the rock has been derived by trans- 
mutation from other rocks. We know of undoubted 
pseudomorphs of hornblende, felspar, augite, &c., con- 
sisting of a substance bearing at least a very close resem- 
blance to serpentine, and actually so called. We will not 
pursue this mineralogical question further, but proceed 
to the description of the rock. 

Serpentine rock consists of two-thirds silicate of mag- 
nesia combined with 12 21 per cent, of water. It also 
contains some protoxide of iron, and this, as well as the 
water, enters into combination with the silica, supplanting 
a part of the magnesia : the proportion of silica varies 
from 38 to 43 per cent. ; the magnesia from 34 to 44 ; 
lime, clay, manganese, bitumen, and carbon are only 



SERPENTINE GROUP. 315 

present in small quantity. The mass is so soft and trac- 
table, and yet so tough, that it admits of being cut into 
various shapes or turned with the lathe. Its unctuous 
feel is a very characteristic property of serpentine, and is 
caused by the great quantity of magnesia which it con- 
tains. Probably the numerous friction surfaces which 
often divide the rock in all directions are also owing to 
the presence of magnesia. These surfaces have a resinous 
lustre and are sometimes striped. The rock is usually of 
a dark-green colour, but some varieties are light-green, 
grey-green, brown, reddish-brown, or almost black, and 
the rock sometimes presents rapid alternation of colour, 
causing spots, flames, or vein-like markings. 

The principal mass of serpentine often porphyritically 
encloses many minerals of various kinds. The most fre- 
quent are pyrope, or magnesia-garnet, sometimes accom- 
panied by talc, less frequently bronzite, schiller-spar, 
chlorite, mica, magnetic iron-ore, pyrites, mispickel, 
chromic iron-ore, and very rarely (in the Ural) native 
platinum. The quantity of magnetic iron-ore is ex- 
ceptionally so considerable, as to influence the magnetic 
needle ; for instance, in the Fichtelgebirge, where, how- 
ever, the rock is not a very characteristic serpentine. The 
mass of serpentine rock is frequently penetrated by veins 
consisting of fibrous serpentine (asbestus), chrysotile, 
chlorite, or picrolite. 

Somewhat more rarely there occur veins or nests of 
calcspar, calcareous magnesian spar, magnesite, saponite, 
pyknotrope, dermatine, talc, brucite, volknerite, horn- 
blende, strahlstein, quartz, chalcedony, jasper, chrysoprase* 
opal, pyrites, chalcopyrite, chromic iron-ore, magnetic 
iron-ore, and native copper. 

Varieties in Texture. 
(a) COMMON COMPACT SERPENTINE. 

IMI-IITER SERPENTIN. (Germ.) 

i-KUPENTINE COMPACTS. (Ft'.) 

(6) PORPHYRITIC SERPENTINE. ) Often with crystals of py- 

PORPHYRARTK5KR SERPENTIN. (Germ.) \ TOPC. 

SERPENTINE PORPHYROU>E. (Fr.) ' 

(c) SLATY SERPENTINE. \ . 

SCHIKFRIGER SERPENTIN. (Germ.) \ Of imperfect thick cleavage. 
SERPENTINE SCHISTEUSE. (Fr.) ) 

(d) VEINED SKKI-KNTINE. 

GBADERTER SERPENTIN. (Germ.) 

SEKPKXTLNE BBECUIVORKE, OPHIOUTHB, Drongniart. (Fr.) 



316 MISCELLANEOUS DIVISION. 

Inasmuch as all serpentine is probably the product of 
the metamorphosis of some other rock, it need hardly be 
said that transition states of this metamorphosis are found 
which differ not only from the extreme result of the pro- 
cess of change the genuine serpentine but from each 
other. If, however, this theory of the origin of serpen- 
tine be well founded, we cannot always succeed in deter- 
mining with certainty the character of the original rock ; 
perhaps in these cases the whole of the rock's mass has 
undergone change, and if bordered by other rocks of a 
different character, no trace is left of its original com- 
position. 

Several of the transition states of serpentine have 
received specific names. 



(e) FORELLENSTEIN (Germ.) or TROUT-STONE, at Neurode, in Silesia. 
A compact labradorite mass, speckled with spots of serpentine, 
which are frequently of angular form, and which Von Rath 
believes to have formerly been crystals of labradorite now 
converted into serpentine. 

(/) RENSLAERITE is the name given by Emmons, in his American 
Geology, 1855, to a serpentine-like rock, somewhat more crys- 
talline than ordinary serpentine. Its colour ranges from greyish 
white to green or black. Specific gravity, 2 - 87 ; composition, 
59'2 silica, 32*9 magnesia, 3'4 protoxide of iron, 1 lime, and. 
only 2-8 water. 

(g) SCHILLER ROCK. \ The name given to a compound of 
SCHILLERFELS. (Germ.) L schillerspar and serpentine, which goes 
j over into ordinary serpentine. It oc- 
curs at the Baste in the Hartz Mountains. It has a serpentine 
matrix enclosing crystals of schillerspar of considerable size. 
It also contains labradorite, augite, mica, chlorite, and pyrites. 
Cocchi proposes that serpentine rocks should be designated 
according to the particular rocks from which they sprang ; e.g. 
diallage-serpentine, diorite-serpentine, granite-serpentine, &c. 
This may be very advisable where it is possible. 



Serpentine for the most part is jointed into irregular, 
massive, or gnarled masses. Exceptionally it is of co- 
lumnar structure, but not unfrequently it shows a kind 
of stratification or tabular jointing. This latter may 
have been occasioned by actual stratification, since ser- 
pentine may well have arisen from stratified rocks. It is 
most frequently found in irregular and subordinate beds 
between strata of crystalline schist, but it also occurs in 



SERPENTINE GROUP. 317 

uncrystalline rocks both in the massive form and in veins. 
The surface of the little round-topped hills which it often 
forms usually shows a very scanty vegetation. 

In some places, as already said, its transmutation from 
other rocks is very evident, as, for instance, from gabbro 
at Siebenlehn, near Freiberg ; from dykes of granite tra- 
versing serpentine rocks near Bohrigen and Waldheim 
in Saxony, where the main serpentine rock itself is not 
improbably a transmuted granulite ; from chlorite-schist 
at Zell, in the Fichtelgebirge, where the change does not 
appear to be yet complete ; and from gneiss (probably), 
or an eklogite rock in the gneiss, at Zoblitz, in the Erz- 
gebirge. The processes and causes of the metamorphosis 
of serpentine are doubtless very different to those of the 
crystalline schists. When serpentine occurs in strata of 
crystalline schist, it is usually of later origin than those> 
and its conversion may have been occasioned by the con- 
tinued infiltration of water, holding magnesia in solution, 
during long periods of time. We are therefore unable to 
class this rock with the crystalline schists any more than 
we can with the igneous or sedimentary rocks. Ac- 
cording to Jukes, many serpentines are metamorphosed 
magnesian limestone. In the Engadine, a serpentine rock 
has been lately found to contain a considerable proportion 
of phosphate, so that it is proposed to use it as manure. 

Serpentine has been recently discovered by Sir Wil- 
liam Logan in the Laurentian limestones of Canada, 
replacing the remains of the foraminiferal organism, 
Eozoon Canadense. 

References. 

Scheerer, Mineral Serpentine, Poggend. Ann. 1854, vol. xcii. 
p. 287. 

Hauf/ht&n, Philos. Mag. 1855, vol. x. p. 253. 

Websky, Krystallstructur des Serpentine, Zeitschr. d. d. geol. 
Ges. 1858, p. 277. 

T. Sterry Hunt, on the Serpentines of Canada and their asso- 
ciated Rocks, Lond. Edin. and Duhl. Phil. Mag. vol. xiv. 
p. 388, 1857. Quart. Jour. Geol. Soc. vol. xxi. p. 67. 

v. Rath, Forellenstein, Poggend. Ann. vol. xcv. p. 652. 

Cocchi, in v. L. u. Br. Jahrb. 1857, p. 600. 

Emmon*, in Americ. Journ. of Sc. 1843, vol. xlv. p. 122. 

A. Streng, Serpentin in Gabbro von Neurode, v. Leonh. u. Br. 
Jahrb. 1864, p. 257. 

C. W. Fuchs, Schillerfels bei Schriestheim, v. Leonh. u. Br. 
Jahrb. 1864, p. 326. 



318 MISCELLANEOUS DIVISION. 



GARNET GROUP. 

The one property which these rocks possess in com- 
mon is, that they all contain garnet as an essential, some- 
times a predominant, constituent. The minerals with 
which the garnet is combined are various, such as am- 
phibole, pyroxene, felspar, mica, dichroite, &c. Garnet 
rocks frequently occur in subordinate masses, often of 
irregular shape and doubtful origin, in strata of crystal- 
line schists, or in granitic rocks. We include in this 
group the following rocks : Eklogite, Disthene rock, 
Eulisite, Garnet rock, Kinzigite, and Dichroite rock. 

45. EKLOGITE, OMPHACITE ROCK, SMA- 
RAGDITE KOCK, DISTHENE ROCK. 

EKLOGIT, OMPHACITFELS, SMARAGDITFELS, DISTHENFELS. 

(Germ.} 
ECLOGITE, OMPHAZITE, Hauy. (Fr.) 

A compound of green smaragdite and red garnet. The 
smaragdite forms a finely crystallised matrix., usually 
somewhat slaty or fibrous, in which the crystals of 
garnet are porphyritically enclosed. 

This rock, to which Haiiy gave the name of eklogite, is 
usually very firm and coherent, difficult to break with 
the hammer. Its fresh fracture presents a peculiarly 
beautiful appearance, from the red garnets sparkling in a 
light-green matrix. Its accessory ingredients cause it to 
vary somewhat in different localities. The beautiful 
eklogites of the district of Miinchberg, in the Fichtel- 
gebirge, sometimes contain mica ; more rarely they con- 
tain zoisite or some other variety of epidote, quartz, 
pyrites, and magnetic iron-ore. In the eklogite of the 
Sau-Alp mountain in Styria, zoisite and actinolite are 
almost its predominant constituents, and it contains in 
addition to the crystals of garnet some quartz, corinthine, 
and disthene. On the island of Syra, the common eklo- 
gite is found in layers or strata, alternating with a rock 
consisting of a compound of disthene-garnet and mica of 
a silvery white colour : this latter rock has been termed 
by Virlet disthene rock ; we might, however, with equal 
propriety, call it a variety of eklogite. A rock occurring 
at HaslaUj near Eger, which has been sometimes called 



GARNET GROUP. 319 

eklogite, consists principally or in great part of idocrase 
(so-called Egeran). 

Eklogite most frequently occurs irregularly imbedded 
in strata of crystalline schist, as, for instance, at Miinch- 
berg, in the gneiss district of that locality. The direction 
of its slaty texture there is in conformity with that of the 
prevailing foliation of the schist, and we may therefore 
doubt whether it should be regarded as a contempora- 
neous formation with the gneiss, or as having forced its 
way into the latter at a subsequent period. Owing to its 
greater power of resistance to the decomposing influences 
of the atmosphere, this rock usually forms prominent 
knolls or rocks. 

Virkt, in the Bullet, de la Soc. geol. 1833, vol. iii. p. 201. 

46. EULISITE. 

EULISIT. (Germ.) 
EULISITE. (Fr.) 

A compound composed of protoxide of iron, resembling 
olivine, green pyroxene, and brownish-red garnet. 

This name was given by A. Erdmann to a rock which 
forms a bed of great thickness in the gneiss at Tunaberg, 
in Sweden. 

Erdmann, Forsok till en geogn. mineral Beskrifing ofver 
Tunabergs Socken, 1849, p. 11. 

47. GARNET ROCK. 

GRANATFELS. (Germ.) 
GRENATITE, Cordier. (Fr.) 

A crystalline granular compound of garnet and horn- 
blende, usually with some magnetic iron-ore. 

Sometimes the brown or yellowish garnet (aplome) 
predominates, so that the mass almost entirely consists of 
a granular aggregate of that mineral ; sometimes, again, 
the rock contains many other minerals besides the horn- 
blende and magnetic iron. 

This rock only occurs in subordinate matter ; e. g. in 
the mica-schist on the Teufelsstein and Klobenstein, near 
Schwarzenberg, in Saxony, where it forms small pro- 
jecting rocks. 

Cotta, Erlauter. z. geogn. Karte von Sachsen. No. 2. p. 225 ; 
v. L. u. Br. Jahrb. 1844, p. 413. 



320 MISCELLANEOUS DIVISION". 

48. KINZIGITE. 

KINZIGIT. (Germ.) 
KINZIGITE. (Fr.) 

A crystalline compound of black mica, garnet, oligoclase, 
sometimes passing over into the compact state. 

This is a rock which was discovered at Wittichen, at 
the Kinzig in the Black Forest. It was formerly con- 
sidered to be a garnet rock and so designated, but H. 
Fischer pointed out its individual properties, and gave it 
a separate name. He afterwards found the same rock at 
Gadernheim and Auerbach, in the Odenwald, and certain 
rocks occurring at Bodenmais in Bavaria and at Cabo de 
Gata in Spain are considered by him to be closely allied 
to it. 

In some of the above-named rocks, cordierite, fibro- 
lite, and mikrocline occur, the last as a substitute for 
oligoclase. 

Fischer, in v. L. u. Br. Jahrbuch, 1860, p. 796 ; and 1861, 
p. 641. 

49. DICHKOITE ROCK. 

DICHROITFELS. (Germ.) 

An irregular compound of felspar, dichroite, garnet, 
and mica (the latter in small quantity) ; firm, dark- 
coloured. 

This rock is allied to dichroite-gneiss. It is found (e.g.) 
forming a dyke in the granite of the Erlbachgrund, near 
Kriebstein, in Saxony. 

Naumann, Erlauter. d. geogn. Karte v. Sachsen, No. 2, p. 13. 

GKEISEN AND SCHOKL GROUP. 

The rocks of this little group are distinguished by their 
consisting principally of quartz, frequently impregnated 
with fine particles of tin-ore, or else associated with beds 
or veins containing tin-ore. In addition to the quartz, 
there occur in these rocks white mica, chlorite, or schorl 
as essential ingredients, and wolfram, specular iron, and 
topaz as accessories. 

The following are the rocks included in this group : 

1. Greisen, a compound of quartz and mica. 



GREISEN AND SCHORL GROUP. 321 

2. Z witter rock, consisting of quartz, chlorite, specular 
iron- and tin-ore. 

3. Schorl rock, a compound of quartz and schorl. 

4. Topaz rock, a breccian variety of schorl rock, with 
topaz. 

50. GKEISEN. 

GREISEN. (Germ.} 
HYALOMICTE, Brongniart. (-F/-.) 

A crystalline granular compound of quartz and mica. 

This, therefore, is granite without felspar, or we may- 
say it is the substance of mica-schist, without its foliated 
texture and conformation. It is of somewhat rare occur- 
rence. It actually passes into granite; that is to say, 
some felspar, or at least kaolin, occasionally enters into 
its composition. But no transitions into mica-schist are 
known ; in other words, it shows no disposition to a fissile 
texture ; it is always distinctly granular (coarse or fine^ 
grained). 

The mica of greisen is chiefly lithia-mica. Some tin- 
L ore likewise occurs as an accessory ingredient, and the 
rock is frequently penetrated with or associated with 
veins of tin-ore, as at Zinnwald, in the Erzgebirge, where 
this rock occurs very characteristically. Less character- 
istically it also occurs near Ober-Pobel, to the west of 
Altenberg. 

Greisen is of massive structure, without a trace of 
stratification. Its constant association with beds and veins 
of tin-ore, in the granite districts of Schlaggenwald, Corn- 
wall, &c., and its resemblance to the zwitter, lead us to 
the conclusion that special circumstances have led to its 
formation from granite by decomposition of its felspar, 
although in the coarse varieties it is difficult to conceive 
how and by what substance the felspar has been replaced. 
In this view we might regard greisen but as a variety of 
granite. We have separately classed it and the other 
tin-bearing rocks in a distinct group, because they pro- 
bably all owe their peculiar properties to special and 
analogous causes,' although these have not yet been satis- 
factorily ascertained. 



322 MISCELLANEOUS DIVISION. 

51. ZWITTEK ROCK. 

ZWITTERGESTEIN, SlOCZWERKSPORPHYR. (Germ.) 

A dark-grey aggregate, rich in quartz, texture fine- 
grained to compact ; its other ingredients are not to 
be distinguished by the naked eye. 

By help of the lens, we may recognise in the fine- 
grained mass of this rock subordinate quantities of chlo- 
rite, tin-ore, arsenical pyrites, and also some micaceous 
iron combined with the quartz. To these the dark colour 
of the rock is probably owing. 

The tin-ore in Altenberg (the only locality where 
the rock is known to occur characteristically) is called 
zwitter, and the rock therefore was called Zwitter rock 
by the miners there. The unsuitable name of Stock- 
werksporphyr is another miners' term, given under the 
erroneous belief that greisen belonged to the porphyries, 
although it has no trace of porphyritic texture. 

The celebrated f pinge ' of Altenberg is a large crater- 
like hollow, formed by the falling in of extensive mining 
works in this rock, which is worked for its tin-ore. At 
the margin of this pinge may be observed the gradual 
transition from fine-grained granite into zwitter rock. The 
granite is first found to be penetrated by numerous and 
very irregular cracks or fissures filled with quartz, and on 
each side of the quartz there is usually a dark stripe of 
from one quarter to one inch thick and upwards. These 
stripes, on closer investigation, are found to be zwitter 
rock, containing no felspar, although they merge gra- 
dually into the surrounding granite, which is of the com- 
mon kind. The stripes are evidently the result of influences 
proceeding from the fissures, and towards the principal 
mine they become broader and broader, so that very little 
unconverted granite is left between the numerous clefts. At 
length the last remnant of the granite disappears, the whole 
mass having been converted into zwitter rock, in which, 
however, the quartz veins still remain distinctly perceptible. 
It would appear that the transmutation must have been 
caused by some solution or vapour impregnated with tin 
penetrating the granite through its many fissures. 

Dr. Rube has carefully analysed several specimens of 
the unchanged granite, of the dark stripes near the quartz, 
and of the entirely converted zwitter rock. From these 



GREISEN AND SCHORL GROUP. 323 

analyses it has appeared that the composition of the dark 
stripes and of the genuine zwitter rock were identical. 
They each contain 3 p. c. silica and 2 p. c. potash less 
than the granite. On the other hand, they contain 
4 p. c. protoxide of iron, 2 p. c. alumina, 0'6 oxide of tin, 
and 0*5 I/O lime more than the granite. It follows, there- 
fore, that in addition to the ingredients which we have 
above mentioned as being recognisable in the zwitter rock 
it must also contain a silicate of alumina. The pene- 
trating solution appears to have decomposed the felspar 
and mica, and in their stead to have formed micaceous 
iron-ore, chlorite, tin-ore, a silicate of alumina, and also to 
have left a deposit of lime. The potash must have been 
carried away in solution ; the silica was probably concen- 
trated, at least in part, in the cleft of the rock, forming 
the veins of quartz which we now see. 

Cotta, in Berg- u. Huttenm. Zeitung, 1860, No. 1, and 1862, 
p. 74. 

52. SCHORLACEOUS SCHIST and SCHORL 

ROCK. 

SCHORLSCHIEFER und ScHORLFELS. (Germ.) 
HYALOTOURMALITHE, Daubrte. (Fr.) 

A crystalline compound of schorl and quartz, foliated 
or granular to compact. 

The schistose varieties are most prevalent, and we have 
therefore placed them foremost ; the compact varieties are 
rare, and in the absence of transition states they are dif- 
ficult of recognition. As accessory ingredients, this rock 
contains mica, chlorite, felspar, tin-ore, arsenical pyrites, 
and exceptionally, in some places, topaz. These schorl 
rocks are (like griesen) almost always accompanied by or 
associated with beds containing tin-ore. The proportion 
of silica which they contain is very unequal, and depends 
on the prevalence of their quartz. 

Varieties in Texture. 

(a) SCHORLACEOUS SCHIST. Its somewhat indistinct foliated texture 
is owing to the parallel disposition or distribution of the acicular 
particles of schorl. The quartz sometimes forms itself into 
contorted layers quite independent of the schistose texture. 
This rock occurs (e.g.) in subordinate beds, alternating with 
mica-schist at Eibenstock, in Saxony, where it is traversed by 
veins of tin-ore. 

T 2 



324 MISCELLANEOUS DIVISION. 

(b) GRANULAR SCHORL ROCK. This is either a tolerably uniform 

compound (fine or coarse-grained) of schorl and quartz ; or it 
consists principally of quartz, with small separate columnar 
particles of schorl, which are frequently broken. 

(c) COMPACT SCHORL ROCK. A blackish-grey mass, in which the in- 

gredients are too intimately blended to be distinguished, as, for 
instance, in the tin mining district of Cornwall. 

Varieties in Composition. 

(d) TOPAZ ROCK. \ Hitherto only known at the Schneck- 

SS^^faT f stein > f t he Voigtland where it 
(/y.) ) forms a dyke of considerable thick- 

ness in the mica-schist. The composition of the rock is sin- 
gular ; large fragments of schorl-schist (containing topaz), with 
quartz, lithomarge, and geodes of topaz, are cemented together 
to a kind of geodic breccia. The rock likewise contains tin- 
ore, apatite, malachite, and azurite as accessories. 

Von Eschwege has given the name of Carvoeira to a quartz 
rock containing schorl, found in the Brazils. 

References. 

Freiesleben, Geogn. Arbeiten, vol. iv. p. 1. 
Breithaupt, Paragenesis, in v. Leonhard's Jahrb. 1854, p. 787. 
oase, Transact, of the Geol. Soc. of Cornwall, 1832, vol. iv. 

pp. 240 and 373. 

Naumann, Erlauter. d. geogn. Karte v. Sachsen, No. 2, p. 201. 
Daubree (Hyalotourmalite), Ann. des Mines, 1841, 3 e ser. 

vol. xx. p. 84. 

CARBONACEOUS GROUP. 

In these rocks carbon is the principal ingredient. They 
are always of dark colour, varying between brown and 
black. They are usually, but not always, combustible. 
They are all of organic origin, and for the most part pro- 
ducts of vegetable accumulation ; some (exceptionally) 
perhaps are the result of the accumulation of animal 
matter. The differences now exhibited are doubtless chiefly 
owing to the degree of metamorphosis of the original 
organic substance. If we start with this assumption, we 
may class these rocks as follows, beginning with those 
whose state is the least changed, and proceeding up to 
those which are most completely metamorphosed : 

1. Peat. The vegetable substance has undergone little 
change. We are not authorised to conclude that all coal 
has been formed from peat-mosses. On the contrary, we 
know of much coal which is the undoubted product of 
trunks and leaves of trees, and various other vegetable 
substances. 



CARBONACEOUS GROUP. 325 

2. Browncoal or Lignite, containing much bitumen. 

3. Common coal (German, Schwarzkohle), containing 
much less bitumen. 

4. Anthracite, containing very little bitumen. 

5. Graphite, without any bitumen, and not combustible. 
Some other differences result from foreign admixtures. 
We observe from the above series that the first process 

of change (from the peat to the browncoal) was accom- 
panied by a development of bitumen, which in the subse- 
quent stages of metamorphosis has again gradually disap- 
peared, and become lost in all probability by evaporation. 
The relative geological ages of the different coals in 
general correspond with and confirm this view ; and the 
only exceptions of which we are aware are capable of 
explanation from special local causes. We may therefore 
say that the varying proportion of bitumen contained in 
the carbonaceous rocks furnishes us with a series which 
at the same time is expressive of their geological age. 

In addition to the above, and in some measure the com- 
plement of the series, we have 

6. Mineral pitch (including asphalte, elastic bitumen, 
and mineral oil) consisting of the bitumen which has been 
volatilised or distilled from bituminous coal. It is some- 
times found separately bedded as a distinct rock, some- 
times as an impregnation of other rocks, such as lime- 
stone, shale, &c. 

The following rocks we add by way of appendix to the 
coal group, as bearing an affinity with it in respect of 
their origin, or otherwise. 

7. Bituminous shale (Brandschiefer), an argillaceous 
shale containing very much bitumen, and frequently car- 
bon. Also, 

8. Kohlenbrandyesteine (burnt clay rocks), which are 
not carbonaceous, but are the result of burning coal upon 
clay rocks. 

9. Guano and coprolite beds. The product of local 
accumulations of animal excrement. 

We have already stated that the usual and normal bed- 
ding of the different kinds of coal entirely corresponds 
with the theory of their origin and of the causes of their 
different composition and structure. The individual ex- 
ceptions only serve to prove the rule ; they may all be 



326 



MISCELLANEOUS DIVISION. 



explained by special circumstances, and when so explained 
are in fact necessary consequences of our assumed theory. 
The following review of the most important coal forma- 
tions will best explain our meaning : 



Age. 

Post Terti- 
ary. 

Tertiary. 



Usual Coal-beds. 

Peat-mosses and beds 
turf in many places. 



of 



Chalk pe- 
riod. 



Oolite or 
Jura pe- 
riod. 



Trias pe- 
riod. 



Coal pe- 
riod. 



Browncoal in North Ger- 
many, Bohemia. Hessen, 
&c. 

Browncoal containing little 
bitumen near Haring, in 
Tyrol (Eocene). 

Browncoal poor in bitumen 
of the Gosau formation 
in the Alps. 

Bituminous shale and coal 
of the Jura and Lias for- 
mations in Germany and 
England. 

Lettenkohle, an impure 
browncoal, containing 
little bitumen, belonging 
to the Keuper formation 
in Germany. 

Common black coal of the 
Coal and Culm forma- 
tions in England, Ger- 
many, and France. 



Transition Anthracite in Scotland and 
or Grey- in Ireland, 
wack e 
period. 

Still older. Graphite in the crystalline 
schists at Passau in Ba- 
varia, &c. 



Exceptional Coal-beds. 



Anthracite (with basalt) at 
the Meissner, in Hessen. 

Ordinary pit-coal or ( black 
coal ' at Silthal, in Tran- 
sylvania. 

Ordinary black coal at 
Ruszkberg, in the Banat. 



Ordinary black coal at 
Fiinfkirchen in Hun- 
gary, and at Steierdorf 
in the Banat. 



Anthracite at Schonfeld, 
Zaunhaus and Brandau, 
in the Erzgebirge, in the 
State of Ohio, adjoining 
the porphyry at Walden- 
berg, &c. 



We see from the foregoing that in every geological 
period in which any sedimentary deposits have taken 
place, there have been accumulations of vegetable matter, 
and that these have (occasionally at least) formed beds, 



CARBONACEOUS GROUP. 327 

and have afterwards become coal. But it is very remark- 
able that as far as those countries which have hitherto 
been geologically explored extend, the principal coal 
formations are confined to two of the great geological 
periods, viz., the Tertiary, to which the browncoals be- 
long, and the Carboniferous, This would be a fact very 
difficult to explain, if it were proved to be true for the 
whole globe ; but as only about one-twelfth part of the 
surface of the earth has been hitherto explored, we may 
be permitted to doubt whether coal may not yet be found 
in large quantity in other formations than those at present 
known. In the interior of Africa, Asia, and Australia, 
and South America, as well as under the ocean, very 
extensive beds of coal may exist, which, together with 
those we already know of the Chalk, Oolite, Trias, and 
transition periods, would fill up all the apparent gaps, and 
furnish as uniform a result with reference to the deposit 
in all ages of material for coal-beds, as of that for any 
other rock. 

According to our present experience, we are authorised 
to believe that the deposit of material for coal formation 
lias taken place in a similar manner and under like con- 
ditions in every period. We accordingly find a certain 
petrographic uniformity or mutual relationship in the coals 
of all ages. The coal-beds are almost universally found 
interstratified and alternating with beds of argillaceous 
rocks and sandstones, usually of grey colour (never red), 
frequently with spherosiderite, or so-called clay-iron- 
stone (Blackband) very seldom with limestone. The state 
of these argillaceous and arenaceous rocks has undergone 
a change corresponding to that of the coal. Their greater 
compactness, solidity, and their laminated texture, almost 
always correspond with the degree in which the bitumen 
has been expelled from the coal, or, in other words, with 
the geological age of the latter. 

53. PEAT, TURF, BOG. 

TORF, DARG. (Germ.) 
TOTJRBE. (Fr.) 

An aggregate of vegetable growth, interwoven and more 
or less compressed and decomposed, of yellow, brown, 
or black colour. 



328 MISCELLANEOUS DIVISION. 

The plants whose remains are usually found in peat 
are of marshy origin, and in Germany usually spring 
from Sphagnum. The moss is more or less compacted, 
felt-like, or almost compact. Sometimes there are found 
imbedded in it trunks of trees, or their branches, roots, 
leaves, hard fruits, and the like ; some of which have 
undergone little or no change. Besides these vegetable 
ingredients, peat frequently contains earthy admixtures, 
also red ochre, nodules of ' kieselguhr ' (an aggregate of 
fossil infusoria), crystallised gypsum and pyrites, or 
earthy particles of vivianite. 

The following varieties are sometimes distinguished, 
though they cannot be definitely characterised and sepa- 
rated: 

() PEAT-MOSS. \ 

FILZ- oder MOOSTORF. (Germ.) \ Loose and felt-like. 

TOURBE FIBREUSE. (Fr.) J 

(6) HEATH-TURF. 

HAJDETORF. (Germ.) 

(c) GRASS-TURF. 

RASENTORF. (Germ.) 

(d) LEAF-TURF. 

PAPIERTORF oder BLATTERTORF. (Germ.) 

(C) Mt . *, } Very wet, and thereby mud-like. 
(/) PITCH-TURF. } Very compact and solid, the vege- 

PECHTORF. (Germ.) I table matter having been much com- 

'</) ! (Lm ' J Passed and transformed. 



Beds of peat and turf are formed or grow before our 
eyes at the present day ; in marshy places we may ob- 
serve the mosses springing and growing out of the graves 
of their predecessors. The beds of moss are found of 
great depth as well as extent ; but they are only known 
on the surface of the earth, and as belonging to the most 
recent geological period. The older beds have been con- 
verted into coal more or less bituminous, only very ex- 
ceptionally, as, for instance, at Miihlhausen, in Thuringia, 
do we find peat of an older date, covered there by diluvial 
loam, not having lost its original character. 



References. 

Wigmann, iiber Entstehtmg, Bildung, and Wesen des Torfes, 

18-37. 
Winkler, iiber Zusaimnensetzung der Torfsorten des Erzge- 

birges, 1840. 



CARBONACEOUS GROUP. 329 

Papius, die Lehre vom Torf, 1845. 

AW, die Entstehung, Gewinnung u. Nutzung des Torfes, 1847. 
Griesbach, Bildung des Torfes in den Emsmoosen, 1846. 
Lutteroth, Umgegend von Miihlhausen, 1848, p. 25. 
Gaudin, Diluvialtorf bei Biarritz, in v. Leonhard's Jahrb. 1857, 
p. 84. 

54. BROWNCOAL or LIGNITE. 

BRAUNKOHLE und LIGNIT. (Germ.) 
LIGNITE. 



A compact or earthy mass, very inflammable, brown or 
black ; streak invariably brown. 

Spec, grav ....... 1'2 1-5. 

Browncoal essentially differs from ordinary black coal 
in containing a much greater proportion of bitumen x 
or the elements which with carbon form bitumen. Hence 
its brown colour and streak, its greater inflammability 
than ordinary coal, and likewise its burning with more 
smoke and smell. Even when very dark-coloured, its 
difference from the ordinary coal may be made to appear 
by boiling its powder with potash-ley, which it will colour 
brown. 

Browncoal contains 55 to 75 p. c. of carbon, with hy- 
drogen, oxygen, and nitrogen, and earthy admixtures in 
very various proportions. Some varieties contain pro- 
portionally little bitumen, and so form transition states 
between brown and black coal. 

The following minerals sometimes occur as accessories : 
amber, mellite, asphalte, gypsum, calcspar, pyrites, and 
lenticular particles of clay-ironstone. 

Varieties in Texture. 

(d) COMMON BROWNCOAL. \ ~ 

GEMEINE DICHTE BRAUNKOHLE, I Compact with dull fracture and 

M i ( KKOHLE. (Germ.) brown colour. 
LIGNITE COMPACTE, Fayet. (Fr.) ' 

(6) EARTHY BROWNCOAL. } -^ ., , . , 

ERDIOE BRAUXKOHLE, STRETCH- [ E ^ pulverised to a brown 



KOHLS. (Germ.) powder. 

LIGNITE TERUEUX. (Fr.) 

(V) RESINOUS BROWNCOAL. ] Very compact and dark, almost 
PECHBRAUNKOHLE. (Germ.) I black, and its fracture shining like 
LIGNITE RESINEUX. (Fr.) 



(d) LIGNITE, BITUMINOUS WOOD. ] Retaining the texture of the 
LIGMT. IIITUMINOSES HOLZ. (Germ.) I original wood from which it 
LIGNITE, orruMiNEux. (Fr.) J w 



330 MISCELLANEOUS DIVISION. 

(e) LEAF COAL or DYSODILE. ) Laminated in consequence 

BLATTERKOHLE, PAPIERKOHLB, oder I O f jt s origin from leaves of 
Lia^S^m^S^uDYsoDiL. (Fr.) \ trees, or of strong pressure 

' of its vegetable particles 
causing a similar effect. 
(/) MOOR COAL. ) 

MOORKOHLE, STREICHKOHLE. L Felt-like and resembling turf. 
LIGNITE PICIFORME. (Fr.) ' 



Varieties in Composition. 

(g) COMMON BROWNCOAL. 

(K) BROWNCOAL WITH LITTLE BITUMEN, to which many of the brown- 
coals of the Alps belong ; e.g. the Molasse coal of Miesbach and 
Tolz, and the Eocene coals of Haring iii the Tyrol. Their ap- 
pearance is very like that of the ordinary black coal, even the 
powder of their streak is very dark, and they only impart a 
weak colour to caustic ley. 

(i) IMPURE BROWNCOAL combined with much earthy matter, passing 
over into bituminous shale. To this class belongs, for instance, 
the so-called Lettenkohle in the lowest division of the Keuper 
formation. 

(k) ALUM EARTH. \ An earthy impure browncoal which con- 

AUUJNERDE. (Germ.) I tains pyrites; and has a tendency to 
decompose into alum and vitriol. 



Browncoal is frequently found in Tertiary deposits, 
exceptionally, however, in older ones ; even in the Ter- 
tiary strata it is sometimes found to have been transmuted 
into anthracite by the influence of heat from adjoining and 
more recent igneous rocks ; as, for instance, at the Meissner, 
in Hessen, where it is found in contact with basalt, or it 
assumes a character very similar to the ordinary black 
coal, as in many Tertiary browncoal beds of the Alps. 

Browncoal may be clearly proved to have had its ori- 
gin in accumulated remains of plants. Some browncoal 
is the product of the conversion of beds of peat and turf, 
some of more distinctly separate plants and parts of plants 
washed together by floods. Subjected to pressure, a slow 
chemical change took place in the mass (the formation of 
bitumen). In some places, under special circumstances, 
this change has proceeded more rapidly than ordinary, and 
thus even in Tertiary strata we find it assuming a cha- 
racter approaching to the state of the ordinary black coal. 

It is hardly necessary to instance localities from 
amongst the very many where browncoal is found in 
Germany and elsewhere. 



CARBONACEOUS GROUP. 331 

References. 
Zincken. Die Braunkohle und ihre Verwerthung. Hanover. 

1865. 
Giimbel, Analysen von Alpenkohlen, v. Leonh. Jahrb. f. Min. 

1864, p. 52. 

55. COMMON COAL, BLACK COAL, or PIT- 
COAL. 

SCHWARZKOHLE oder STEINKOHLE. (Germ.} 
HOUILLE. (Fr.) 

A compact black mass, in fresh fracture usually of resinous 
lustre ; streak black, usually friable ; not so inflam- 
mable as browncoal, but, like it, burns with Jlame, 
smoke, and smell. 
Spec. grav. .... V .' 1'3 1-6. 

The substance of coal is principally carbon. It has less 
of the elements of bitumen (oxygen, hydrogen, and ni- 
trogen) than browncoal, but more than anthracite. It 
forms a transition state between browncoal and anthracite, 
and occasionally goes over into each. Like browncoal 
and peat, it contains more or less earthy matter, by 
which its value is depreciated. The following minerals 
occur as accessories in coal : Pyrites, clay-ironstone (in 
nodules or septaria), gypsum and calcspar ; frequently 
also clumps of fibrous anthracite, stone-coal (Werner's 
' mineral charcoal ' ). 

Jukes observes : < In many ordinary coals little flakes 
of mineral charcoal occur, retaining that part of the vege- 
table structure called the vascular tissue. They are 
called " mother of coal " by the colliers, in some places. 
It is frequently seen in the form of a thin silky coating, 
covering some of the surfaces of the coal. Its powder is 
black, and if boiled with caustic ley, it scarcely colours 
the latter.' 

In coal districts a very great number of different kinds 
of coal are distinguished according to their special values 
for use ' indeed their varieties are often as numerous as 
the different seams of a coal-field, and even the different 
beds of a compound seam are readily distinguished from 
each other by the colliers, who give particular names to 
them ; and even small blocks of these varieties can be 
recognised by them and identified with the seam or part 
of a seam from which they are derived. Neither are 



332 MISCELLANEOUS DIVISION. 

these distinctions, which are only to be perceived after 
long practice, unimportant, since these varieties have dis- 
tinct qualities; some of them being better adapted to 
smelting, and said to be " good furnace-coal ; " some of 
them to blacksmith's work, or " good shop-coal ; " others 
to various uses ; while only a few comparatively are best 
fitted for domestic purposes, and are brought to market 
by the coal-merchant.' Jukes. 

6 Some idea of the immense varieties of coal may be 
gained from an inspection of the Admiralty Coal Investi- 
gation (Mem. Geol. Survey, vol. i.), as well as from the 
varying qualities of those we are in the habit of using 
daily in our houses. As many as seventy denominations 
of coal are said to be imported into London alone. 

( All these minute varieties are commonly included 
under four principal heads : 1. Caking Coal-, 2. Splint 
or Hard Coal] 3. Cherry or Soft Coal:, and 4. Cannel 
or Parrot Coal. 

f Caking Coal is so named from its fusing or running 
together on the fire so as to form clinkers, requiring fre- 
quent stirring to prevent the whole mass being welded 
together. It breaks commonly into small fragments, with 
a short uneven fracture. The Newcastle coal, and many 
others from different localities, are caking coals. They 
leave many cinders, and a dark dirty ash. 

' Splint or Hard Coal is well known in the Glasgow 
coal-field. It is not easily broken, nor is it easily kindled, 
though when lighted it affords a clear, lasting fire. It 
can be got in much larger blocks than the caking coals. 

6 Cherry or Soft Coal is an abundant and beautiful 
variety, velvet black in colour, with a slight admixture of 
grey. It has a splendid or shining resinous lustre, does 
not cake when heated, has a clear shaly fracture, is easily 
frangible, and readily catches fire. It leaves compara- 
tively few cinders, and its ash is white and light. It 
requires little stirring, and gives out a cheerful flame and 
heat. The Staffordshire coals principally belong to this 
variety. 

( Cannel or Parrot Coal is called cannel, from its burn- 
ing with a clear flame like a candle ; and parrot, in Scot- 
land, from its crackling or chattering when burnt. Can- 
nel coal varies much in appearance from a dull earthy to 



CARBONACEOUS GROUP. 333 

a brilliant, shining, and waxy lustre. It is always com- 
pact, and does not soil the fingers. Its fracture is some- 
times shaly, sometimes compact. The bright shining 
varieties often burn away like wood, leaving scarcely any 
cinders and only a little white ash. The duller and more 
earthy kinds leave a white ash, retaining nearly the same 
size and shape as the original lumps of coal. Cannel coal 
often takes a good polish, and can be worked into boxes 
and other articles. Jet is an extreme variety of cannel 
coal in one direction, as batt or carbonaceous shale is in 
another. ' Jukes. 

In Germany the varieties have been thus classed : 



) 



(a) GEMEINE STEIXKOHLE, or common Black Coal, compact with 

resinous lustre. 

PECHKOHLE (or Pitch-coal), compact with resinous lustre. 
KANNELKOHLE (GAGAT), Cannel coal. 

(d) SCHIEFERKOHLE, a bituminous shale, sometimes composed of 

alternate layers of common coal and anthracite. 

(e) RTTSSKOHLE (Sooty Coal), an earthy variety, dirty to the touch, 

apparently consisting of a compound of common coal and 
anthracite. 

The origin of coal as a product of vegetable substances 
is well established. The texture of the original plants 
may sometimes be discovered under the microscope. Beds 
of turf or parts of plants accumulated by flood- water have 
furnished the material. Geinitz has even endeavoured to 
explain the different structure of many coal-beds by the 
differences of their original vegetable substance. At 
Zwickau, in Saxony, and a few other places, he has dis- 
tinguished the following varieties : 

(a) FARNENKOHLE (Fern-coal), formed principally of ferns. To this 

class belong the four uppermost notz of resinous coal (Pech- 

kohle), at Oberhohndorf, many coals of Wettin, Lobejiin 

and Ilmenau in Germany. 
(/3) CALAMITENKOHLE (Calamitan Coal). To this the Russkohle 

of Zwickau belongs, also the so-called mineral charcoal. It 

is always very anthracitic and siliceous. 
(y) SIGILLARIENKOHLE (Sigillarian Coal). To this belong the 

Planitzflotz, and the deep ' Pechkohle ' near Zwickau. 
(<;) SAGENNARIENKOHLE (Sagennarian Coal). To this belong, e.g., 

the older coals of Hainichen and Ebersdorf, in Saxony. 

The following are the principal typical varieties in 
France, according to Leplay : 



334 MISCELLANEOUS DIVISION. 

(A) HOUILLE SECHE. 

(B) HOIJILLE MAKECHALE. 

(C) HOUILLE GKASSE. (Caking coal.) 

(D) HOUILLE MAIGEE. 

Coal chiefly occurs in separate beds or subordinate 
strata in the sandstone and argillaceous shale of the Coal 
formation. It occurs, however, with very similar rocks 
in somewhat older and in much younger formations. 
Thus, for instance, at Hainichen in the Kulm formation, 
near Fiinfkirchen, in Hungary, and Steindorf, in the 
Banat, in the Lias formation ; at Ruszkberg, in the Banat, 
between strata of the Chalk formation ; and in Silthal, in 
the southern boundary of Transylvania, even in Tertiary 
strata. The existence of black coal in these more recent 
formations is to be accounted for by exceptional geological 
circumstances, which have accelerated the process of 
transmutation. The character of the plants themselves 
may also have contributed to this result. We find that 
the remains of Calamites have usually been converted into 
siliceous anthracite ; and it is very possibje that the parti- 
cular nature of the original plant-substance may have 
affected the character of the coal in many other respects. 
In certain localities again, the eruption of recent igneous 
rocks have occasioned special phenomena of transmuta- 
tion ; as, for instance, at Waldenburg, in Silesia, where 
the porphyries have locally converted ordinary black coal 
into native coke or anthracite. 

Jukes observes : ( Microscopical examination exhibits 
not only the vascular, but the cellular tissue of plants in 
the substance of many coals, as was shown by Mr. 
Witham in his work on the structure of fossil plants, and 
by many observers since. All coals have a peculiar 
structure, which bears a slight analogy to crystallisation. 
They break or split, not only along the bedding, but 
across it, along two sets of planes at right angles to the 
bedding and to each other. The smooth clean faces pro- 
duced by one of those cleavage planes are more marked 
and regular than that produced by the other, as may be 
seen by examining any lump of coal. The principal of 
these division planes are called by the colliers the face 
of the coal, the other being called the back, or end, of the 
coal. They preserve their parallelism sometimes over 



CARBONACEOUS GROUP. 335 

very wide areas ; and the mode of working or getting the 
coal, and the direction of the galleries, is governed by the 
direction of the face. 

' It is a structure which is probably the result of the 
mineralising process undergone in passing from an or- 
ganic to an inorganic state, and may be likened perhaps 
to the " cleavage " of a mineral rather than to either the 
true " slaty cleavage" of rocks, or to their " foliation" or 
"jointing."' Jukes, p, 134. 

References. 

Tenney has contributed numerous analyses to the New York 

Mining Magazine, 1856, p. 15. 
Dawson, iiber die Pflanzenstructur der Steinkohle, in v. L. u. 

Br. Jahrb. 1860, p. 571. 
Neivberry, Entstehung der Cannelkohle, in v. L. u. Br. Jahrb. 

1858, p. 852. 
Geinitz, Die Versteinerungen der Steinkohlenformation in 

Sachsen, 1855, and Geogn. Darst. der Steinkohlenformation in 

Sachsen, 1856. Geologic der Steinkohlen Europas. Miinchen, 

1865. 
Goppert, iiber die Bildung der Steinkohle, im 4. Deel xx. 

Tweede Verzammling von naturkundige Verhandlingen 

Ton de Hollandische Maatschappij d. Wetenschappen te 

Haarlem. 

v. Lemhard in the deuts. Vierteljahresschrift, 1838. 
Stein, Untersuchung der Steinkohlen Sachsens, 1857. 
Ronald and Richardson, Chemical Technology, vol. i. p. 30, &c. 
Lovetz, Mineralien in fossilen Brennstoffen, v. Leonn. Jahrb. 

1863, p. 654. 

56. ANTHKACITE. 

ANTHRACTT oder GLANZKOHLE. (Germ.) 
ANTHRACITE. 



Slack with vitreous to half-metallic lustre, friable, streak 
black, not easily ignited, and burns almost without 
smoke and smell. 

Spec, grav ...... . 1-5 1'7. 

Anthracite consists almost entirely of carbon, and con- 
tains very little hydrogen, oxygen, or nitrogen ; that is to 
say, it is almost free from bitumen a native compact coke. 
It contains earthy admixtures in various quantity, as is 
the case with other coal. It also contains the following 
accessory ingredients : pyrites, clay-ironstone, gypsum, 
or calcspar in clefts. 

There are scarcely any special varieties of anthracite to 



336 MISCELLANEOUS DIVISION. 

describe, unless we consider as such the transition states 
between anthracite and common coal and the compounds 
of the two with each other. 

Extensive beds of anthracite are only met with in the 
formations of the Greywacke (transition) and Carboni- 
ferous periods. Locally, anthracite is sometimes asso- 
ciated with browncoal. As a rule, beds of anthracite are 
never met with in the Coal formation except in localities 
where it appears to have been exposed to special plutonic 
influences, as at Zaunhaus, Schonfeld, and Brandau in the 
Erzgebirge, Sable and Beaulieu in Marne (France), at 
the Stangen Alp in Styria, at Osnabruck, and in the 
Alleghany Mountains. The normal position of anthracite 
appears to be in the transition formations. 

We are not aware of any treatises or works specially devoted 
to the subject of anthracite. Much, however, respecting it will 
be found in those cited under the head of coal. 

57. GRAPHITE, PLUMBAGO. 

GRAPHIT. (Germ.) 
GEAPHITE. (Fr.} 

A greyish-black aggregate, consisting of graphite ; texture 
varying from flaky to compact ; soft, gives a black 
streak (like lead pencil), greasy feel, not inflammable, 
on the contrary capable of resisting fire. 

Spec, grav 1-92-2. 

Graphite or plumbago is carbon in a state nearly pure, 
but differing very widely from that of the diamond. As 
a rock, graphite contains admixtures of silica, clay, oxide 
of iron, or sometimes small crystalline grains of other 
minerals. By these admixtures its properties are, how- 
ever, only slightly altered. 

Graphite is the last member of the series of transmuta- 
tion of the carbonaceous rocks, and is therefore principally 
(and normally) found in subordinate beds in strata of 
crystalline slate-rocks or as a local admixture in the same 
rocks ; at Passau in Bavaria, in Bohemia, at Borrow- 
dale in England, &c. It occurs exceptionally in granite, 
and is even found to fill fissures in that and other rocks. 

We might theoretically regard the diamond as a still 
more perfect, that is to say more crystalline and purer 
product of transmutation of the carboniferous series. Its 
occurrence is however so rare, and so subordinate, that 
we cannot here notice it further. 



CARBONACEOUS GROUP. 337 

References. 

Pntisep, Graphite, Calcutta Gleanings of Science. Edin. Phil. 

Journ. 1832, vol. xxvi. p. 346. 

Glocker, Graphit, Erdmann's Journ. f. Chem. vol. vi. p. 330. 
Rcgnault, Graphite, Ann. des Mines, 3e Se>. vol. xii. p. 161. 
Herter, Graphitschiefer mit Pflanzenresten, Zeitsch. d. deut. 

geol. Ges. vol. xv. p. 459. 
Respecting the localities of the occurrence of Graphite, refer 

to v. L. u. Br. Jahrb. 1833, p. 552 ; 1836, p. 595; 1838, p. 

427; 1839, p. 448; Journ. d. Phys. vol. xliv. p. 301 ; Cor- 

respondenzbl. des zool. mineral. Vereins zu Regensburg, 1827. 

p. 29, and 1848, p. 158. 

58. BITUMEN and MINEKAL PITCH. 

BITUMEN und ERDPECH, ASPHALT. (Germ.} 
BITUMJE, MALTHE, ASPHALTE. 



A pitch-like mass, colour varying from dark-brown to 
black) softens with heat. 

Spec. grav. bitumen ..... 0-7 0*9 
Mineral pitch ...... 1-1 1-2 

This bituminous mass consists of 80*82 carbon, 910 
hydrogen, and 8*9 oxygen and nitrogen. 

Bitumen is very seldom found in mass in the interior 
of the earth, but frequently as an accessory admixture in 
calcareous, marly, or argillaceous rocks. On the surface 
of the earth it occasionally forms small pitch lakes, as at 
the Dead Sea, and in the island of Trinidad. To this 
class belongs the petroleum, or rock-oil, which in North 
America has been recently found streaming in great 
abundance from the earth. 

The origin of bitumen may be, and probably is, two- 
fold. Bitumen or the gaseous elements of bitumen must 
of necessity be disengaged where bituminous coals un- 
dergo transmutation into coals of a less bituminous cha- 
racter, or into anthracite. This bitumen may either 
permeate the neighbouring rocks and make them bitu- 
minous, or it may rise to the surface of the earth and 
become a separate deposit of a fluid or semi-fluid sub- 
stance. Again, bitumen will be formed wherever animal 
remains gasteropods, fishes, and the like have been 
enclosed by stratified beds of rock, and have become 
transmuted. And thus some limestones, marls, or clay- 
rocks may have become bituminous (being converted into 
oil-slate, stinkstein, &c.). Or the bitumen contained in 

z 



338 MISCELLANEOUS DIVISION. 

such rocks may, under the influence of heat or other 
causes, again escape and become deposited elsewhere. 

The occurrence of bitumen in nature, taken in con- 
nection with the animal and vegetable fossils found in 
coal, completes the evidence in support of the established 
view of the origin of coal. 

Mayer's Asphalt des Val de Travers, 1839, is the only sepa- 
rate treatise on bitumen known to us. On rock-oil springs in 
North America, Tide Petermann's Mittheilungen, 1861, vol. iv. 
p. 151 : and Kane's Zeitschrift d. Erdkunde. 1862, vol. xii. 
p. 279. 

59. PYROSCHIST(#ww), BITUMINOUS SHALE. 

BRANDSCHIEFER. (Germ.) 

SCHISTE BITFMINEUX, MARNOLITE, Cordier. (Fr.) 

Is the name given to very bituminous and thereby dark- 
brown or black-coloured argillaceous shale, which, 
although, it burns in five, yet, owing to its containing 
so much clay, cannot itself be used as fuel. 

These are best classed with the carbonaceous rocks, 
together with which they frequently appear, and for which 
they have sometimes even been mistaken. Their streak 
is of resinous lustre ; they often contain distinct remains of 
plants or fishes ; sometimes bitumen may be extracted 
from them, and they are then sometimes called oil-slate 
( Oelschiefer, Germ.; Schiste oleifere, Fr.). 

Bituminous shales of this class are found in Germany, 
especially in the lower Rothliegende, e.g. at Oschatz, in 
the Lias of Wiirtemburg, and in the chain of the Weser, 
and in the Brown-coal formation at many places. 

Sterry Hunt, Bitumen and Brandschiefer (Pyroschist), Silliman 
and Dana's American Journal, vol. xxxv. p. 157. 

Appendix. 

We may here add the burnt clays and the beds of 
guano or coprolites. The first because they have ori- 
ginated from the burning of coal-beds, the latter as accu- 
mulations of organic matter. 

60. BUENT CLAYS. 

GEBRANNTE THONE, KOHLEISTBRANDGESTEIKE, ERDSCHLACKEU 

und PORZELLANJASPIS. (Germ.) 
THERMANTIDE, Cordier. (Fr.) 



CARBONACEOUS GROUP. 339 

These are local products of transmutation from clay 
rocks produced by burning coal-beds. They are too un- 
like in character to admit of a common definition. We, 
therefore, separately describe a few principal varieties. 

(a) BURNT ARGILLACEOUS SHALE. ) Hard, and resembling 



GEBRAN-NTER SCHIEFEHTHON. (Germ.) I buck-colour, yellow, 

AK.IILK acmonusE MfcTAMORPHiQUE. (Fr.) 



nevertheless, still exhibiting the original laminated texture, 
and impressions of plants of the slate-clay. At Planitz, near 
Zwickau, in the Coal formation, and at Zittau in Saxony, in 
the Browncoal formation. 

(&) ROCKSLAG. \ By reason of greater heat the lami- 

ERDSCHLACKE, KOHLEXBRAND- I n ated texture has been destroyed. 

OLA SE BJ gSj (<?erm I and a scoriaceous slag-like texture 

' arisen. Colours similar to the 

burnt argillaceous shale. Found in the same localities. 

(c) PORCELAIN JASPER, PORCELANITE. J The clay mass is half vi- 

PORZELLAXJASPIS. (Germ.) I trefied, porcelain-like, of 

J greasy lustre, pearl-^rey, 
bluish-grey, lavender-blue, or brown. The same localities. 

61. GUANO and other COPROLITE BEDS. 

GUANO und andere KOPROLITHENLAGER. (Germ.) 
GUANO. (Pr.) 

These deposits must also be enumerated amongst rocks. 
In some localities they occupy a considerable place in the 
earth's crust. 

(a) GUANO. 1 Forms earthy white, grey, or yellowish- 

GUANO. (Germ.) L brown accumulations of very disa 
GUANO. (Fr.) J smell It ig chie{]y known ag ft 



upon certain rocky islands of tropical climates. It consists 
chiefly of the excrement of birds, and contains, according to 
Boussingault, about 50 53 organic matter and ammonia-salts, 
19 20 phosphate of lime, 3 phosphoric acid, 7 alkali, 1 2 silica 
and sand, and 15 16 water. These accumulations attain a depth 
of more than 100 feet, and frequently contain many other 
organic remains of recent date. 

References. 

v. Etzel, in Gumprecht's Zeitschr. f. Erdkunde, vol. v. pp. 326 

and 425, vol. vi. p. 152. 

Tifhm, in Petermann's Geogn. Mittheilungen, 1859, p. 173. 
Bvu**imi<iHlt, in Compt. rend. 1860, vol. li. p. 844 j v. L. u. Br. 

Jahrb. 1861, p. 206. 
Sandberger, Sombrero Phosphat (Guano), v. Leonh. Jahrb. 1864, 

p. 631. 
Jenisch, Guano verschiedener Lander, v. Leonh. Jahrb. 1864, 

p. 866. 

Z2 



340 MISCELLANEOUS DIVISION. 

(b) COPROLITE BEDS. ] Composed of excrements of fishes, reptiles, 

KOPROLITHENLAGER. , and mammalia which inhabited caverns, 
J some portions entirely petrified, but yet 
containing much phosphoric acid. Found in many sedimentary 
strata, also in caverns. 

(c) BLACK EARTH. ] May also be enumerated in this place, 

SCHWARZERDE, TscHOR- I although the 6 9 per cent, of organic 
NOSEM. (Germ.) j admixtures con tained in this black 
clayey earth do not altogether appear to have been derived from 
excrement. In Southern Eussia this formation covers a great 
extent, and lies on the surface of the earth. It attains a maxi- 
mum depth of twenty feet. If subjected to the strong pressure of 
overlying strata, it might possibly turn into bituminous shale. 

References. 

Murchison, Geology of Russia, 1845, p. 547. 
Schmid, in v. L. u. Br. Jahrb. 1850, p. 350. 
Wangenlieim v. Qualen, ibid. 1856, p. 75. 



IRONSTONE GROUP. 

These are rocks principally consisting of minerals rich 
in iron, so called iron-ores ; these ores contain hydrated 
oxide of iron, peroxide of iron, protoxide of iron, or car- 
bonate of protoxide of iron, and accordingly are re- 
spectively termed brown hematite, red hematite, magnetic 
iron, and spathose or sparry iron. Of these varieties there 
are many modifications both of structure and composition. 
We append to this group pea-iron-ore (Bohnerz) a pisi- 
form spherosiderite which consists of a silicate of protoxide 
of iron. 

These different ironstones occur in the form of strata 
or layers, veins or irregular masses, imbedded between 
other rocks of various geological antiquity. The different 
ironstones themselves, however, have a certain difference 
of geological character which may be expressed somewhat 
as follows : 

Hydrated Oxide of Iron, or Is sometimes an original formation and 

Broicn Hematite, sometimes a secondary product. It 

occurs in the form of layers, veins, or 

irregular masses in formations or rocks 

of every age. 

Peroxide of Iron. Red He- Is in most cases undoubtedly a secon- 

matite. dary product. It occurs in the form of 

veins, layers, or irregular masses, but 

usually only in the older formations 

and rocks. 



IRONSTONE GROUP. 341 

Peroxide and Protoxide of Forms layers, veins, or irregular masses ; 
Iron (combined} or Mag- these only in the crystalline schists 
netic Iron-ore. and plutonic igneous rocks. Fre- 

quently occurs also as an impreg- 
nation in the volcanic rocks. 

Carbonate of Protoxide of As clay-ironstone, it forms layers or 

Iron, or Cathode Iron. concretions, principally in the Coal 

formations ; as spathic iron, it forms 

veins and irregular masses in various 

different rocks. 

Pea-iron ore (Bohnerz). Fills cavities and depressions in lime- 

stones. 



62. BROWN HEMATITE. 

BRAUNEISENSTEIN. (Germ.) 
LIMONITE, Beudant. (Fr.} 

A compact earthy, porous, or fibrous aggregate of brown 
iron-ore (limonite), yellowish-brown to black with 
brown streak. 

Brown hematite consists entirely, or at least essentially, 
of hydrated oxide of iron (Fe*H 3 ) containing 85*6 per 
cent, oxide of iron and 14 '4 water. It sometimes, how- 
ever, contains admixtures of oxide of manganese, silica, 
clay, or lime. 

Varieties in Texture. 
(a) COMPACT BROWN HEMATITE. 

GEMEIXER DICHTER BRAUXEISENSTEIN. (Germ.) 

LlMOXlTE COMPACTS. (Fr.) 

(6) SCALY AND OCHRT BROWN IRON-ORE, YELLOW OCHRE. 

ERDIGEB BRAUNEISENSTEIN, oder EISEXOCKER. (Germ.) 
OCRK JAUNE. (Fr.) 

(c) FIBROUS BROWN IRON-ORE, or GLASKOPP. ] Occurs only in 

FASRIGER BRAUNEISENSTEIN, oder GLASKOPF. (Germ.) i subordinate 
HEMATITE mum CONCRETIONNEE FIBREUSE. (Fr.) j qua ntities, as 

stalactite. 

(d) REXIFORM IRON-ORE. ] Rounded concretions of brown 

NIEREXERZ, REKERZ, STOCKERZ. L iron-ore, chiefly found in clay, 
J and usually occurring in com- 
bination with 

(e) PEA-ORE. 1 Made up of globules (about the size 

BOHNERZ. (Germ.) I o f peas), mostly of concentric struc- 

M^^AI EN GRA^-S. (Fr.) J ^ ^Ael in a mass of clay, 
iron-ochre, or limestone. 
(/) OOLITIC BROWN ORE. ] Occurs in the form of 



/ tioiis. 



342 MISCELLANEOUS DIVISION. 

(ff) BOG-ORE. A Whicli likewise differs in the 

RASENEISENSTEIX, SUMPFERZ, QUELL- mo & e o f jt s occurrence from 

55 R .)' WIESENERZ ' Ll - other varieties. It is a porous 

MINERAIS DE MARAIS, LIMOXITE. j arenaceous deposit of brown 

( Fr '^ iron-ore on the earth's surface, 
and is created by springs or stagnant water. Frequently con- 
tains some phosphoric acid. 

Varieties in Composition. 

(h) A. VARIETY RICH IN MANGANESE, \ , 

BLACK IRONSTONE. Frequently quite black, 

MANGANREICHEB BRAUNEISENSTEIN, f therefore sometimes called 
ScHWARZEisExsTErN. (Germ.) black ironstone. 

LlMONITE MANGANESLFERE. (Fr.) > 

(i) AN ARGILLACEOUS VARIETY (BROWN OR YELLOW CLAY-IRON- 
STONE). 

THONREICHER BRAUNEISENSTEIX, THOXEISENSTEIX. (Germ.) 

(k) A SILICEOUS VARIETY, PASSING INTO BROWN FERRUGINOUS 
QUARTZ. 

KlESELREICHER BRAUNEISEXSTEIN. (Germ.) 

HEMATITE BRXJNE SIUCEUSE (JASPOIDE). (Fr.) 

All these different varieties (with the exception of bog- 
ore, which only occurs on the surface of the ground) fre- 
quently form subordinate beds or veins filling up clefts in 
other rocks. Sometimes, but more rarely, they form local 
massive and irregular accumulations especially at the con- 
tact of two different rocks (contact formations). 

Bog-ore is formed at the present day as a chemical 
precipitate from water holding salts of iron in solution ; 
this process is occasioned or accompanied by decomposition 
of organic substances. If we suppose similar deposits of 
brown hematite to have taken place in former periods, 
and then to have been covered by other sedimentary 
formations, we may easily conceive how in process of 
time the thin compact layers of iron-ore which we find 
imbedded in other strata would have arisen. Sometimes 
brown hematite is evidently a product of transmutation 
from spathic iron, or even magnetic iron-ore. 

63. EED HEMATITE. 

ROTHEISENSTEIN. (Germ.) 
HEMATITE ROUGE. (Fr.) 

A compact, earthy., or fibrous, or sometimes crystalline, 
slaty, aggregate of red iron-ore ; colour red to black ; 
streak red. 
Spec. grav. 4 5. 

Red hematite consists entirely or essentially of peroxide 



IRONSTONE GROUP. 343 

of iron (70 p. c. iron + 30 p. c. oxygen), sometimes inti- 
mately combined with oxide of manganese, silica, or clay. 
Its crystalline state is termed specular iron (Eisenglanz), 
or micaceous iron (Eisenglimmer). 

Varieties in Texture. 

(a) COMMON RED HEMATITE. \ 

GEMEINER DICHTER ROTHEISENSTEIN. I ComDact 

(Germ.) 
HEMATITE ROUGE COMPACTS. (Fr.) > 

(b) EARTHY HEMATITE, or RED IRON-MOULD. 

ERDIGER ROTHEISENSTEIN, oder ROTHER EISENMULM. (Germ.) 

(c) FIBROUS HEMATITE, REDDLE. 

FASRIGER ROTHEISENSTEIN, ROTHEL oder ROTHER GLASKOPF. (Germ.) 
HEMATITE ROUGE FIBREUSE. (Fr.) 

(d) OOLITIC HEMATITE, or FERRUGINOUS OOLITE. 

OOLTTHISCHER ROTHEISENSTEIN, Oder ElSENOOLTTH. (Germ.) 

HEMATITE ROUGE OOLITHIQUE. (Fr.) 

(e) MICACEOUS IRON-SCHIST. 1 Consisting of a schis- 

EISENGLIMMERSCHIEFKU. (Germ.) I tosc acTgregate of mica- 

1 Kit OUGISTE ECAILLEUX OU MICACE. (Fr.) I ceous ij. on e g QU the 

Gorgeleu in Marmaros, in Hungary, where it is imbedded 
between strata of chlorite-schist and "limestone. 

(f) SPECULAR IRON. 'j As rock, an aggregate of specular 

i:isKxuLA>-zoEOTEix. (Germ.) I i r() n (iron-glance), usually combined 
PER SPECULAIRE. (Fr.) J ^ ^ f^ Qf J^ ^^ 

rence as a rock ; e.g. on the Island of Elba, and at Picton-nob, r 
in North America. 

Varieties in Composition. 

0) A VARIETY RICH IN MANGANESE r Whence its black 

(BLACK HEMATITE). J colour ; sometimes 

MANGANHEICHER ROTHEISENSTEIN (SCHWARZ- 1 called black hematite 

UiiMATITK MANCrAVKSIF^RE (Fr} V OCll\VflJ*ZGlSCllSLClD ) 

(A) RED CLAY-IRONSTONE, RED OCHRE. 



THONREICHER ROTHEISENSTEIN (THON- L An arefillaceous vanety. 
(Germ.) J 



OCRE ROUGE. (Fr.) 

(i) SILICEOUS HEMATITE. \ 

KlESELREICIIER ROTHEISEN- I T j. J f 

RBV. (Germ.) f Passing into red ferruginous quartz. 

HEMATITE ROUGE SHJCEUSE 
(JASPOtoE). (Fr.) I 

(K) ITABIRITE. \ A compound of specular iron, micaceous 

ITABIRIT. (Germ.) I iron, magnetic iron-ore, and some quartz ; 

' .) granular, schistose, or compact. As acces- 

sories, it contains talc, chlorite, actinolite, and native gold. 

Found at Itabira, in Brazil (v. Eschwege, ' Brasilien '). 

(7) TOPANHOACANGA (MooRSHEAD ROCK). This rock consists of 
angular or somewhat rounded fragments of specular iron, mi- 
caceous iron, and magnetic iron-ore, cemented together by a 
ferruginous compound. Sometimes it also contains fragments 
of quartz, itacolumite, clay-slate, &c., rarely also, grains of 
native gold. At Itabira. Villa Rica, and Marianna, in Brazil, 
it forms a crust on the surface of the ground of from four to 
twelve feet thick. 



344 MISCELLANEOUS DIVISION. 

Most of the above-mentioned varieties of red hematite 
occur in stratifications or veins, like the brown hematite ; 
and they are also (though more rarely) found irregularly 
massed between other rocks, usually of the transition or 
crystalline schist formations never those of very recent 
origin. 

We may, perhaps, be justified in regarding the red 
hematites as products of catogenic transmutation from 
brown hematite ; yet it would appear that they have some- 
times been formed from spathic iron under special circum- 
stances. Certain it is from their anhydrous state we may 
safely say that they are never original deposits from 
aqueous solution, although they sometimes contain dis- 
tinct fossils. 

Specular iron, or iron-glance (as a mineral), is some- 
times found in the clefts or fissures of volcanoes, where 
it is a product of sublimation. 

64. MAGNETIC IRONSTONE, MAGNETITE. 

MAGNETEISENSTEIN. (Germ.} 

MAGNETITE, FEE OXYDFLE, Hauy and Dufrenoy. (-FV.) 

A granular or compact aggregate of magnetic iron-ore ; 
black ; streak black ; metallic lustre ; influences the 
magnetic needle. 

Spec, grav 4-5 5-2. 

Pure magnetic iron-ore consists of 69 to 75 per cent, 
peroxide of iron, and 31 to 25 per cent, protoxide of iron 
(therefore it contains about 72 per cent. iron). As a rock 
it occurs mixed with specular iron, chlorite, chromic iron- 
ore, titanic iron-ore, pyrites, chalcopyrite, quartz, horn- 
blende, augite, garnet, or felspar, &c. 

Varieties in Texture. 
(a) GRANULAR. 
(6) COMPACT. 

(c) SCHISTOSE. The foliation is occasioned by admixture of foreign 

minerals. 

Varieties in Composition. 

(d) PUKE MAGNETIC IRON-ORE. 

(e) CHLORITIC MAGNETIC IRONSTONE. 

(/) CHROMIC IRONSTONE, in which chromic iron predominates or 

forms the only ingredient. 
(g) GARNETIFEROUS IRONSTONE ; passing over into garnet rock. 



IEONSTOXE GROUP. 345 

(h) PYRITO-MAGNETIC IRONSTONE. 

(i) CATAWBIRTTB is the name given by 0. Lieber to a rock found 

by him in South Carolina, occurring there in great abundance. 

It consists of a compound of talc and magnetic iron, intimately 

blended together. 

Magnetic ironstone forms subordinate beds or veins in 
the crystalline schists. It is very extensively developed 
at Schmiedefeld, in the Thuringian Forest, at Arendal in 
Norway, at Danemora in Sweden, as a stratum in the 
clay-slate at Berggieshiibel in Saxony. Chromic iron- 
stone is usually associated with serpentine. 

65. SPATHIC IRON; SIDERITE. 

SPATHEISENSTEIN. (Germ.) 

FER CARBONATE, Haily ; SIDEROSE, Seudant. (Fr.) 

A granular or compact aggregate of spathic iron ; yel- 
lowish-white, grey, or yellowish-brown; streak white; 
effervesces with acid. 

Spec. grav. . * . - . . f 37 3-9. 

Spathic iron is carbonate of protoxide of iron (62 per cent. 

protoxide of iron, and 38 carbonic acid) ; where it occurs 

as a rock it is sometimes mixed with ankerite, calc-spar, 

clay, specular iron, copper pyrites, &c., in small quantities. 

Varieties in Texture. 

(a) GRANULAR. 

(b) VERY FINE-GRAINED. 

(c) COMPACT SPHEROSIDERITE (CLAY- \ So called from its oc- 

IRONSTONE). I curring in the form of 

DICHTER SPATHEISENSTEIN, SPHAROSIDERIT. j spheroidal concretions 

<<*-> J orsentaria 

SIDEROSE COMPACTS. (Fr.) U1 8e p l ' ttilt| " 

(d) A SHALY VARIETY OF SPHEROSIDERITE, Or CARBONIFEROUS 

IRONSTONE (BLACKBAND). 

SCHIEFRIQER SPHAROSIDERIT, Oder KOHLENEI8ENSTEIN. (Germ.) 

Varieties in Composition. 

(e) ROHWAND (Germ.). A granular spathic ironstone, mixed with 

much ankerite or calcspar. 

(f) ARGILLACEOUS SPHEROSIDERITE, \ 

or CLAY IRONSTONE. I Also called clay carbonate 

THONREICHER SPHAROSIDERIT, oder J O f i ron< 

SEPTARIA AROILEUX. (Fr.) ' 

(g) CARBONIFEROUS IRONSTONE, BLACKBAND. \ Dark-coloured by 

KHHLENEISKNOTEIN. (Germ.) v reason of admixture 

J of coal j usually a 
slaty spherosiderite or clay ironstone (d). 



346 MISCELLANEOUS DIVISION. 

This is the black "band of Scotland. < This natural admixture 
of coaly matter confers on these rocks their special value, the 
raw stone being readily calcined, in fact igniting and slagging 
itself without the expensive admixture of coal, as is the case 
with the ordinary clay ironstones and hematites.' Page. 
Mushet makes a distinction between Blackband and Clayband, 

Berg- u. Huttenm. Zeit. 1863, p. 295. 

The crystalline varieties occur as subordinate strata, 
veins or regular masses, in the crystalline schists or the 
older sedimentary formations. The compact spherosi- 
derites are most usually found with beds of coal. The 
origin of these stratified beds and irregular masses of 
spathic iron has not hitherto been satisfactorily explained, 
since a carbonate of protoxide of iron could not be de- 
posited under atmospheric influences. Probably the car- 
bonic acid may have supervened at a later period. On 
the other hand, the influence of the air will quickly change 
spathic iron into brown hematite, and hence it is that 
we find the surface of spherosiderite usually coated with 
a brown crust, and many entire beds of brown hematite 
appear to have been formed in this manner. A different 
process of mutation may, perhaps, in some cases, have 
produced red hematite and magnetic iron-ore. 

Appendix. 

66. DISILICATE OF PROTOXIDE OF IRON. 

HALBKIESELSATJRES EISENOXYDTJL. {Germ.} 
CHAMOISITE (Chamoison, Valais). (Fr.} 

This compound sometimes occurs in the form of pea-iron-ore 
contained in ferruginous clay, together with nodules of jasper, 
as, for instance, at Kandern, on the western margin of the 
Schwarzwald in Germany. 
Deffner, zur Erklarung der Bohnerzgebilde, Stuttgart, 1859. 

67. SILICEOUS SPHEROSIDERITE. 

KIESELIGER SPHAROSIDERIT. (Germ.) 
CARBONATE DE FER SILICETJX. (Fr.~) 

This is a rock, described by Naumann, of a peculiar and fine 
arenaceous character, consisting essentially of spherosiderite 
(containing manganese) and siliceous earth or quartz-sand. It 
forms a stratum (very rich in fossils) in the Nummulite forma- 
tion of the Bavarian Alps between Traunstein and Sonthofen. 
Schafthautl, in v. L. u. Br. Jahrbuch, 1846, p. 664. 



347 



CHAPTER V. 

MINERALS AS ROCKS. 

WE have in the first three chapters treated of those 
rocks which, by reason of their great extent and volume, 
may be regarded as the principal ingredients of the earth's 
crust. We have seen that they are mostly of compound 
character, although some few are essentially simple mine- 
ral substances. 

In this place we propose to enumerate those simple 
minerals which appear as local accumulations in different 
parts of the globe, forming essential members of particu- 
lar formations, sometimes as stratified beds, sometimes as 
veins or dykes, or irregular masses ; their volume being 
just sufficient to entitle them to be considered* as members 
of the rock family, taking an independent part in the 
structure of the solid crust of the earth, although in 
comparison with the other rock-formations which we have 
hitherto treated, their bulk is for the most part very 
inconsiderable. 

A description of the formation, texture, &c., of these 
mineral rocks will, in most cases, be unnecessary, as they 
must be mineralogically determined and recognised. We 
shall, therefore, in each case only give the name of the 
mineral, adding some short remarks as to its exceptional 
lithological character. 

68. ICE. 

Eis. (Germ.} 
GLACE. (Fr.) 

Sometimes compact, sometimes granular , fibrous or lami- 
nated. 

We need not here describe the properties of ice, but it 
is not unimportant to consider the conditions under which 
perpetual ice occurring in large masses forms part of the 
solid crust of the earth. 

The snow which falls in the polar regions, and in 



348 MINERALS AS EOCKS. 

mountain districts above the snow-line, only partially 
thaws in summer ; the remainder accumulates year by 
year. The successive falls of snow form a series of super- 
jacent strata, the fleecy mass becomes consolidated by 
pressure, and grains of ice are formed which unite into a 
stratified granular ice ; this in the Alps is called firn or 
neve. The masses of neve thus formed glide gradually 
down over the mountain slopes and precipices into the 
ravines and valleys. In the course of their downward 
movement their stratification becomes much contorted 
and otherwise disturbed ; they are, moreover, transformed 
from distinctly granular neve into indistinctly granular 
ice, or so-called glaciers. 

The glacier continues to glide with a slow movement 
down the valley. Its lower extremity, thus arrived in 
warmer regions, thaws more rapidly and equalises the 
accumulation of snow pressing down in fresh masses from 
above. Hence the general extent and size of the glacier 
usually remains much the same, although the individual 
parts are constantly changing their position. By the mo- 
tion of the glacier the traces of original stratification be- 
come more and more contorted and effaced. The glacier, 
moreover, becomes rent with frequent fissures (crevasses), 
and in these the water arising from occasional thawing 
accumulates and freezes during night or winter into new 
ice, which may be distinguished from the genuine glacier 
ice by its more compact structure. 

All these phenomena are very instructive, and afford 
many analogies to other rock formations and transfor- 
mations. From loose accumulations, by means of pressure 
and consolidation, masses are formed which become firmer 
and more solid, and at last tolerably compact. Strata 
are bent, pushed out of place, and overturned. The mass 
is torn by cracks and fissures, which are filled by water 
rendered fluid by heat. This freezes and constructs ice 
veins in ice, somewhat like granite veins in granite, only 
that these latter were probably filled from below, and 
under a much higher temperature. By a kind of weather- 
ing process even the compact venous ice in its turn be- 
comes granular or separates into thin columnar parts, and 
all these changes take place before our eyes in compara- 
tively short spaces of time. 



MINERALS AS ROCKS. 349 

Very similar phenomena occur on a much larger scale 
in the polar regions ; only they are less accessible, and 
therefore more difficult of observation. 

Besides these permanent masses of ice lying on the 
surface of the earth, there occur in the northern plains of 
Siberia extensive underground ice strata of great thick- 
ness, sometimes interstratified with beds of sand, or they 
contain sand mixed with the ice, and occasionally these 
strata are covered with a surface layer of soil, which 
during the short summer of Siberia supports vegetation. 

69. OPAL. 

OPAL. (Germ.) 
OPALE. (Fr.) 

As a rock, usually only forms very subordinate masses, 
e.g. the so-called vitrite, which occurs at Meronitz, in 
Bohemia, and contains numerous py ropes. 

If, however, we reckon under the name of opal all the 
various amorphous silicates enumerated by Naumann, we 
find amongst them several very important rocks : 

Varieties. 

(a) SiLiCEOU8 SINTER, or SILICEOUS TUFF. "| Stratified incrustations 
KIESKUSINTER Oder KiESELxcFF. (Germ.) i- and porous masses ; 

J found as a deposit of 

hot springs in Iceland and Kamtschatka, and, according to Hoch- 
stetter, still more frequently in New Zealand. (Novarareise, 
1862, vol. iii. p. 165.) 

(6) SEMI-OPAL. \ Forms independent deposits, e. g. at Bilin, 

HALBOPAL. (Germ.) I in Bohemia ; also irregular fillings of clefts 
MB-OPALK. (Fr.) ) ^ ^^c rocks, e. g. at Hanau on the 
Maine, in the dolerite. 

(c) MENILITE. t Menilite occurs in the Paris basin in clumps 

HEXTUT. (Germ.) 1 and beds. It is found there in gypsuin and 
rat (Fr.) { in marl ( Eocene ) . in Auvergne, in fresh- 
water marl (Miocene). 

(d) POLISHING SLATE, TRIPOLI. ] Consists of small shell-shaped 

POLIRSCHIEFER, SAUGscHiEFER, KLEB- [ particles of silica of a peculiar 
Tmp^ F ??;J Rn>PEU (<7m "' ) I form, only to be distinguished 

' with the aid of the micro- 
scope, so-called siliceous armour of Diatomacece or Infusoria ; 
Nuiiinann therefore calls it Diatomeenpelit. Ehrenberg reckoned 
that the polishing slate of Bilin m Bohemia contained in 
a cubic inch 41,000 millions siliceous shells of Gattlonella. 
Each individual is invisible to the naked eye, so that when 
used for polishing metallic surfaces it produces only fine in- 
visible scratches. Distinction is made in Bohemia between 



350 MIXEKALS AS KOCKS. 

tlie polirscliiefer (soft, friable, not adhering to the tongue) and 

sangschiefer (adhering to the tongue and more solid, probably 

because it is impregnated with opal substance). Both are 

only known in very recent deposits; the older ones have 

probably been transmuted into hornstein or lydian stone. 

(Ehrenberg, Fossil Infusoria, Berlin, 1837, and Mikrogeologie.) 

(e) KIESELGUHR. '| The same substance as polishing slate, 

EJESELGUHR. (Germ.) [ b u t more dust-like, earthy, generally 

^^^551 white or yellow. Found in beds many 

* feet thick in the turf deposits at Soos, 

near Franzensbad, Bohemia. The rock called RANDANITE by 

Salvetat belongs to this species ; it consists of a white powder. 

(v. L. u. Br. Jahrb. 1848, p. 124.) 

70. QUARTZ. 

QUARZ. (Germ.} 
QUARTZ. (Fr.) 

Occurs as an essential ingredient in many rocks, but it 
also occurs as an independent rock in many varieties, 
some of which are of considerable extent. We repeat the 
mention in this place of several quartz rocks which we 
have already noticed and included in other groups. 

Varieties. 

(a) ROCK CRYSTAL and AMETHYST. \ Sometimes the essential 

BERGKRYSTALL und AMETHYST. (Germ.) I ingredient of veins and 
CRYSTAL DE ROCHE et AMETHYSTE. (Fr.) I J^Lgg 

(b) COMMON QUARTZ. ) Forms independent bed-veins or irre- 

QUARTZ COMMUN. (Fr.) ) gular masses. Quartz -schist, see p. 
246, ante ; Quartz -breccia, p. 305 ; Quartz-sandstones (siliceous 
sandstone), p. 296. Millstone-quartz, freshwater-quartz, or 
lemon-quartz, are porous varieties resembling chert, which, 
. according to the fossils occasionally found in them, have been 
deposited by fresh water, as, e. g., the celebrated millstones of 
the Paris basin (Quartz meulier). 

(c) FERRUGINOUS QUARTZ. j Yellow, red-brown, or black : forms 

EISENKIESEL. (Germ.) [ transition states into iasper. Its 

QUARTZ FERRUCHNEUX. (Fr.)) mode o f occurrence in nature is the 
same as that of ordinary quartz. 

(d) HORNSTONE, CHERT. ") Compact, forms independent beds, 

HORNSTEIN; HORNFELS. (Germ.) [ veins, and masses. In Germanv 
J thenameofHornfelsispivento 

certain rocks, the product of transmutation of argillaceous 
deposits, and found adjoining to plutonic rocks, to which they 
probably owe the change they have undergone. 

(e) LYDIAN STONE, or LYDITE, BLACK j Contains carbon which 

CHERT. I gives it a greyish colour 



KIESELSCHIEFER oder LYDIT. (Germ.) inclining to black 

QUARTZ LYDIEN. (Fr.) ) ^ gtratified in thin 



laminse, and hence of a laminated texture ; generally pene- 
trated by numerous white veins of quartz j much rent by 



MINERALS AS ROCKS. 351 

angular fissures, sometimes containing lenticular concretions, 
and also sometimes containing laminae of clay-slate. In 
fissures it contains wavellite, calaite, variscite. It occurs with 
tolerable frequency as a subordinate stratum in clay-slate, 
slate-clay, or even mica-schist. 
(/) JASPER. \ Compact, variegated, frequently striped or 

JASPIS. (Germ.) I flamed (riband -i asper, agate-jasper). Much 

JASPE. ( r.) j ^^ ^ een ca |i e( j jasper which properly belongs 
to the feLsitic rocks, even to the felsitic tufis. It forms subordi- 
nate layers imbedded in other rocks, and nodular concretions. 
Jasper may be readily distinguished from petrosilex (which it 
otherwise sometimes resembles) by the fusibility of the latter. 
(g) AGATE. j The name given to certain combinations of 

ACHAT. (Germ.) L chalcedony, carnelian, amethyst, and quartz. 

AGATE. (Fr.) j There ^ mftny varieties : _i,anded agate, 

fortification-agate, coral-agate, &c. It frequently forms veins or 
fills cavities in other rocks. 

(h) FLINT. \ Very similar to hornstone, but half amor- 

FEUEROTETS. (Germ.) L phous, chiefly yellow, brown, grey, or 
J black. Forms nodules, and then are fre- 
quently disposed in layers ; very frequent, e. g. in chalk. 

71. CORUNDUM. 

KORUND oder SCHMIRGEL. (Germ.) 
CORINDON. (Fr.) 

Forms fine-grained subordinate layers imbedded in 
crystalline schists, frequently accompanied by magnetic 
iron-ore. Ochsenkopff, in the Erzgebirge ; Gumuchdagh, 
in Asia Minor ; Naxos ; Chester, Massachusetts. 

72. FLUOR-SPAR. 

FLUSSSPATH. (Germ.') 
FLUORINE, SPATHFLTJOR. (Fr.) 

Frequently an essential ingredient in metalliferous 
veins. A compact aggregate of fluor-spar forms a rock 
at Rottleberode and Strassberg in the Hartz Mountains. 

73. ROCK-SALT. 

STEINSALZ. (Gtrm.) 
SEL GEMME. (Fr.) 

Chloride of sodium occurring as a rock is usually crys- 
talline-granular, white, translucent or transparent, 
easily soluble in water, and possesses a saline taste. 

Spec, grav 2-12-2. 

Pure chloride of sodium consists of 60 per cent, chlorine 
to 40 per cent, sodium. In nature, however, it almost 
always contains sulphate of lime, chloride of calcium, 



352 MINERALS AS HOCKS. 

chloride of magnesium, and other salts ; frequently ad- 
mixtures of bitumen, clay, or boracite. Salt itself some- 
times only forms an ingredient of some clays (Salzthon, 
saliferous clay). 

The colour of rock-salt is variable ; it is sometimes 
yellow, red, bluish, or greenish, by reason of small ad- 
mixtures of oxide of iron. 

Varieties. 

(a) GRANULAR ROCK-SALT. 

KORNIGES STEINSALZ. (Germ.) 

SEL GEMME GRANULAIRE. (Fr.) 

(b) SPARRY ROCK-SALT. 

BLATTRIGES STEINSALZ. (Germ.) 

SEL GEMME LAMrNTAIRE (SPATHIQUE). (Fr.) 

(c) FIBROUS ROCK-SALT. 

FASRIGES STEINSALZ. (Germ.) 
SEL GEMME FIBREUX. (Fr.) 

(d) KNISTERSALZ. (Germ.) 

(e) GRUNSALZ, SPIZASALZ, SZYBIKER SALZ. (Germ.') 

Reference. 

The origin of the rock-salt of Strassfurt, near Magdeburg, has 
been lately treated in a masterly manner by F. Bischof, Die 
Steinsalzwerke zu Strassfurt, 1864. 

74. TKONA. 

TRONA. (Germ.) 
SESQUI-CARBOKTATE DE SOUDE. (Fr.) 

Occurs in Fezzan, in North Africa, forming a rock 
which is even used for building purposes. 

75. ALUNITE, or ALUM STONE. 

ALTJNIT, oder ALAUNSTEIN. (Germ.) 
ALTJNITE. 



Forms a rock in the neighbourhood of Tolfa, near 
Civita Vecchia. (See p. 185.) 

76. BARYTES, or HEAVY SPAR. 

BARYT, oder SCHWERSPATH. (Germ.) 
BARYTINE, ou SPATH PESANT. (Fr.) 

This mineral, which forms an essential part of many 
metalliferous veins, was discovered by Yon Dechen, as 
constituting a compact rock forming a bed some ten feet 
in thickness, in the clay-slate of Meggen in the Lenne- 
thal. Its colour was dark-grey. 



MINERALS AS ROCKS. 353 

Karsten's Archiv, 1845, vol. xix. p. 748 ; see also v. Hoinm- 
gen, Verb, der naturh. Ver. d. pr. Rheinl. 1856, vol. xiii. p. 
300 ; Sandberyer, geol. Verb. d. H. Nassau, p. 11 j and Zim- 
mermann, Harzgebirge, 1834, voL i. p. 151. 

77. BORACITE, or STASSFURTITE. 

BORACIT, STASSFURTIT. (Germ.) 
BORACITE, STASSFURTITE. (Fr.) 

Forms irregular layers imbedded in the rock-salt of 
Stasfurt. 

Zeitschr. d. d. geol. Ges. 1856, voL viii. p. 156. 

78. PHOSPHORITE. 

PHOSPHORIT. (Germ.) 

CHAUX PHOSPHATEE, APATITE. (Fr.) 

Sometimes forms compact spheroidal masses, or sub- 
ordinate layers, and even dykes or veins. Krageroe in 
Norway. 

79. CRYOLITE. 

KRYOLITH. (Germ.) 
CRYOLITE. (Fr.) 

Forms considerable veins in the granitic gneiss at 
Evigtok, in Greenland. (Journ. of Geol. Soc.) 

80. ARAGONITE. 

ARAGONIT. (Germ.) 
ARAGONITE. (Fr.) 

Many so-called calcareous sinters and peastones consist, 
properly speaking, not of calcspar, but aragonite. (See 
p. 281.) 

81. ANKERITE. 

ANKERIT. (Germ.) 
ANKERITE. (Fr.) 

This is most frequently found mixed in subordinate 
quantities with spathic iron (vide p. 345, ante) ; and is 
sometimes found separately as an independent rock. 

82. MAGNESITE. 

MAGNESIT. (Germ.) 
MAGNKSIE CARBONATEE. (Fr.) 

Frequently forms compact masses, but of subordinate 
size and extent. 

A A 



3o4 MINERALS AS ROCKS. 

83. DIALLOGITE, CARBONATE OF MANGA- 

NESE. 

MANGANSPATH. (Germ.') 
DIALLOGITE. (Fr) 

Frequently forms the principal constituent of metal- 
liferous veins, e.g. at Kapnik, in Hungary. 

84. MALACHITE. 

MALACHIT. (Germ.) 
MALACHITE. (Fr.) 

Sometimes forms great clumps or masses in beds of 
copper-ore in Russia. 

85. TALC, or STEATITE. 

TALK oder SPECKSTEIN. (Germ.) 
TALC ou STEATITE. (Fr.) 

Forms independent compact beds, e.g. at Gopfers-Griin, 
in the Fichtelgebirge, where it forms a rock which can- 
not be classed as a talc-schist. 

86. MEERSCHAUM. 

MEERSCHAUM. (Germ) 

ECUME DE MEK, MAGNESITE. (Fr.) 

Forms separate beds in Natolia, Negroponte, Crimea, 
&c. 



87. AGALMATOLITE, or FIGURE-STONE. 

AGALMATOLITH oder BILDSTEIN. (Germ.) 
AGALMATOLITHE. (Fr.) 

The principal member of a dyke or vein at Dilln, near 
Schemnitz. Also in China. 

88. KAOLIN, or PORCELAIN CLAY. 

KAOLIN oder POKZELLANERDE. (Germ.) 
KAOLIN. (Fr.) 

This is probably everywhere merely a product of the 
decomposition of rocks very rich in felspar. Aue, in 
Saxony, where it is a decomposed granite. In some 
places a slight change has converted it into clay. 



MINERALS AS ROCKS. 355 

89. LITHOMARGE. 

STEIN MARK. (Germ.) 
LITHOMARGE. (Fr.) 

Is found in very subordinate quantity between other 
rocks. 

90. ORTHOCLASE. 

ORTHOKLAS. (Germ.) 
ORTHOSE. 



Sometimes forms independent dykes and accumulations, 
e. g. in the granite at Carlsbad. 

91. PYCNITE. 

PYKNIT. (Germ.) 
PYCNITE. (Fr.) 

Forms concretions and dykes in the Zwitter rock, at 
Altenberg, in Saxony. 

92. EPIDOSITE, or PISTACITE ROCK. 

EPIDOSIT oder PISTAZITFELS. (Germ.) 
EPIDOSITE. (Fr.) 

Epidote usually combined with some quartz. A sub- 
ordinate formation in the Island of Elba. 

93. LEPIDOLITE, or LITHIA-MICA. 

LEPIDOLITH oder LITHIONGLIMMER. (Germ.) 
LEPIDOLITE (MiCA A LITHINE). (Fr.) 

Forms an independent rock of fine-grained and foliated 
texture, e. g. at Rozena, in Moravia. 

94. ROCK SOAP. 

BERGSEIFE. (Germ.) 
PIERRE DE SAVON. (Fr.) 

Occurs in masses of subordinate extent, e. g. at Bilin, 
in Bohemia. 

95. BOLE. 

BOL. (Germ.) 
BOLE. (Fr.) 

Occurs in masses of subordinate size in many limestone 
rocks. 

96. FULLERS' EARTH. 

WALKERDE. (Germ.) 
TERRE A FOTTLON. ^(Fr.) 

AA 2 



356 MINERALS AS ROCKS. 

A substance resembling clay, somewhat greasy, but not 
in the smallest degree plastic, but falling to pieces in 
water, usually of yellowish green colour; is probably a 
product of the decomposition of basic igneous rocks. 
Cilli in Styria ; Nutfield, near Reigate. 

97. FERREO-LITHOMARGE. 

EISENSTEINMARK. (Germ.) 
TERATOLITE. (Fr.) 

Occurs in subordinate masses at Zwickau, in Saxony. 

98. YELLOW EARTH, or MELINITE. 



GELBERDE. (Germ.} 

Occurs in small accumulations at Amberg, and other 
places. 

99. GALMEY, CARBONATE OF ZINC (in part). 

GALMEI. (Germ.} 
CALAMINE. (Fr.} 

This name is indifferently applied to both the principal 
zinc-ores : the silicate of zinc and the carbonate of zinc. 
They occur together, and they form aggregates of con- 
siderable size in the dolomite limestones of Tarnowitz, 
Iserlohn, Aix-la-Chapelle, &c. 

100. RHODONITE (in part), MANGANESE SPAR 

(Bisilicate of Manganese). 

KIESELMANGAN oder MANGANKIESEL. (Germ.} 
RHODONITE (MANGANESE SILICATE). (Fr.} 

Occurs (e. g.) in subordinate beds at Rosenau, in 
Hungary; Cummington, Massachusetts, U.S. 

101. LIEVRITE, or ILVAITE. 

LIEVRIT. (Germ.} 
ILVAITE. (Fr.} 

Occurs (e.g.) in subordinate beds in the mica-schist of 
the Island of Elba. 

102. MANGANESE-ORES. 

MANGANERZE. (Germ.} 
MINERAIS DE MANGANESE. (Fr.} 



MINERALS AS ROCKS. 357 

One or more of these form veins of considerable thick- 
ness, or beds of irregular shape, at Ilmenau, Ilfeld, 
Kleinlinden, Warwickshire, &c. 

103. RED ZINC-ORE. 

ROTHZINKERZ. (Germ.) 

MlNERAI ROUGE DE ZlNC (FRANKLnrTTE) . (Fr.) 

Combined with Franklinite forms a bed of very con- 
siderable thickness at Franklin, in New Jersey. 

104. GALENA. 

BLEIGLAKZ. (Germ.) 
GALENE. (Fr.) 

Usually associated with blende and sulphurets ; forms 
veins of considerable extent and thickness, and occurs 
otherwise in separate beds.. 

105. ANTIMONY-GLANCE. 

ANTIMONGLANZ. (Germ.) 
ANTIMOINE. (Fr.) 

Forms veins of considerable thickness, e.g. at Magurka, 
in Hungary. 

106. ARSENICAL PYRITES. 

ARSENKIES. (Germ.) 
PYRITES ARSENICALES. (Fr.) 

Usually associated with other sulphurets ; occurs in 
separate formations of considerable thickness. 

107. MARCASITE, or HYDROUS PYRITES. 

MARKASIT oder WASSERKIES. (Germ.) 
MARCASSITE. (Fr.) 

Forms subordinate layers imbedded in other rocks, e. g. 
in the Browncoal formation at Littmitz, in Bohemia. 

108. PYRITES. 

ScnWEFELKIES 

PYRITES. (Fr 
Usually associated with some chalcopyrite ; forms beds, 



ScnWEFELKIES, PYRIT. (Germ.) 
PYRITES. (Fr.) 



358 MINERALS AS ROCKS. 

veins, or irregular masses of considerable size, e.g. at 
Domokos in Transylvania, Rio Tinto in Spain, Schmoll- 
nitz in Hungary, Groslar at the Hartz, Fahlun in Sweden, 
Agordo in the Alps. 

109. CINNABAR. 

ZINNOBER. (Germ.} 
CINABRE. 



Occurs but rarely in beds of considerable size or thick- 
ness, e.g. at Almaden in Spain, Idria, California. 

110. SULPHUR. 

SCHWEFEL. (Germ.') 

SOTTERE. 



Forms rounded concretions and layers, in marl forma- 
tions, e.g. at Radoboj in Croatia, Sicily, Perticara in 
Umbria. 



359 



PART III. 

OBSEEVATIONS ON THE PROCESSES OF 
ROCK FORMATION IN NATURE. 

THE NATURAL PROCESSES by which rocks have been 
formed and are still in course of formation are partly in- 
dicated in the foregoing pages. The following are those 
known to us from actual observation : 

1. CONSOLIDATION OF SUBSTANCES FROM A STATE 
OF IGNEOUS FUSION BY PROCESS OF COOLING. This 
is the process which all lavas undergo, and by which, pro- 
bably, all igneous rocks have been formed. We must 
assume that a first crust of the earth was likewise so 
formed, but we cannot with certainty point to any of the 
rocks remaining to us at the present day as representing 
this primeval formation. 

2. DEPOSIT OF SUBSTANCES FROM A STATE OF SUS- 
PENSION IN WATER, AND OF SUBSTANCES FALLEN 
THROUGH THE AIR. Thus are formed the sedimentary 
rocks, under which general designation every kind of de- 
posit is included. 

They may be divided as follows : 

(a) Mechanical deposits (actual sediments). To this 
class belong deposits of mud, sand, and pebbles of every 
kind, which by process of condensation and cementa- 
tion produce argillaceous shale, clay-slate, limestone, 
sandstone, conglomerate, and other similar rocks. 

From the atmosphere are deposited particles of dust 
and sand. These are frequently held in a state of 
suspension for a considerable time, and transported by 
the wind to great distances. Volcanoes vomit detached 



360 PEOCESSES OF ROCK FORMATION: 

substances or fine particles of dust, which with the aid 
of water form volcanic tufas of various kinds. 

(b) Chemical precipitates from aqueous solutions. 
By chemical agency many kinds of deposit are formed. 
For instance, calc-tuff, siliceous tuff, bog iron-ore, in- 
crustations of salt, and many mineral formations in 
clefts and cavities of rocks. The crystalline particles 
of ice which fall from the air in the form of snow may 
be considered as a chemical precipitate. Snow, as 
we have seen, forms the neve and glaciers of high 
mountain regions. 

(c) Zoogenic deposits are products of animal agency. 
Their massive accumulation is partly a mechanical pro- 
cess. Thus we have rocks formed entirely of siliceous 
infusoria, also the chalks, banks of shells, coral-reefs, 
guano and coprolite beds, &c. 

From the condensation of these rocks, hornstone, 
lydian-stone, limestone, &c., may have resulted. 

(d) Phytogenic deposits are such as consist chiefly of 
vegetable substances ; these have either grown in situ, 
or have been washed together. From these deposits, by 
process of consolidation and subsequent conversion, the 
different coal formations have resulted. 

The above-mentioned processes of rock-formation are 
those which admit of direct observation. There are others 
at whose nature we only arrive by reasoning from the 
results. Such are : 

3. METAMORPHOSIS, OR TRANSMUTATION or PRE- 
VIOUSLY EXISTING ROCKS. This is a process constantly 
at work it has even begun to affect most of the dis- 
tinctly sedimentary rocks. Few of these but have under- 
gone some change. Thus the changes from argillaceous 
mud to shale and then to clay-slate, from sand to sand- 
stone, from loose stones to conglomerate, from calcareous 
silt to limestone, from peat-moss to browncoal, or ordinary 
black coal, &c., are, properly speaking, all cases of meta- 
morphosis, although the rocks we have just named are not 
usually termed metamorphic. That term is reserved 
for the further stages of transmutation, where the change 
is so complete that the first state of the rock can no longer 
be easily or with certainty recognised by mere observa- 



IGXEOUS ROCKS. 361 

tion. The genuine metamorphic rocks are mica-schist, 
gneiss, and the other crystalline schists, whose identity 
with their originals can only be proved by deduction 
from a variety of collateral circumstances. 



The foregoing, are the only processes of rock-formation 
known to us by observation, or which can be ascertained 
by deduction from known facts. These processes are, 
however, undoubted and indisputable, and our chief diffi- 
culty consists in determining in each instance to which 
mode of formation a rock owes its origin. Here many 
difficulties and justifiable doubts present themselves. Let 
us therefore attempt the application of these experiences 
and their consequences to the several groups of rocks 
which we have described in the preceding pages. 



IGXEOUS EOCKS. ' (Eruptiv-Gesteine.) 

No unprejudiced observer of geological phenomena can 
doubt that those which we have classed and named as 
igneous rocks were once in a fluid or viscous state, and 
that whilst in that state they broke through pre-existing 
rocks, overflowed them, and afterwards consolidated. 
Ample proofs of these operations of nature are found in 
the relation of the bedding of the igneous to those of their 
surrounding rocks, the disturbances which they have fre- 
quently (but not invariably) caused in the rocks broken 
through, the fragments of the latter which they enclose, 
and the veins or branches which they have thrust into 
those adjoining. These general conditions established, 
there still remain many special phenomena of formation 
to be explained and accounted for, which we propose 
briefly to consider in this place. 

The great mutual resemblance of all igneous rocks 
both chemically and mineralogically bespeaks a like pro- 
cess of formation for all, i.e. they were all forced upwards 
from the interior towards the surface of the earth in a 



362 PKOCESSES OF EOCK FOKMATIOX : 

molten state, like the lavas (which are evidently igneous 
products) from the active volcanoes of the present ^day. 
But although the composition and mode of occurrence of all 
these rocks is, generally speaking, of a very uniform cha- 
racter, yet special differences show that a great part of 
those which are now exposed to our view did not originally 
reach the surface and overflow at the time of their up- 
heaval in the manner of genuine lavas, but became solid 
at a considerable depth underground, where they still were 
covered by or imbedded between other rocks ; and we 
must assume that their present appearance on the face of 
the earth is owing to subsequent destruction and wash- 
ing away of the superincumbent rocks. Hence we dis- 
tinguish between volcanic and plutonic rocks. The vol- 
canic (as we have seen) are those which are known, or 
supposed, to have consolidated at or near the surface ; and 
the plutonic those which are presumed to have solidified 
at a considerable depth in the interior of the earth. 
There is no definite depth of measurement which we can 
fix as a boundary between these two kinds of formation ; 
the question of such depth must remain a subject for 
entirely speculative estimate. Nor is the division of 
rocks into volcanic and plutonic dependent on their mere 
age, although in most cases it corresponds to a certain 
extent in fact with their relative antiquity, because most 
of the older volcanic formations have decayed away and 
disappeared, whilst the newer plutonic formations have 
not yet been laid bare, and are therefore inaccessible to 
our view. The deeper in the earth that any rock was 
formed, the longer would be (cceteris paribus) the time 
necessary for its denudation ; and therefore the older will 
it be when we meet with it at the surface. 

Recent chemical analysis (as we have already had oc- 
casion to remark) shows a great uniformity of elementary 
composition in all classes of igneous rocks. We have 
seen that they all consist of silica, alumina, peroxide 
or protoxide of iron, lime, magnesia, potash, and soda, 
and frequently some water. Their other ingredients 
are but subordinate in quantity, and can only be re- 
garded as accessory ; such are protoxide of manganese, 
titanic acid, carbonic acid, phosphoric acid, sulphuric 



IGNEOUS KOCKS. 363 

acid, oxide of chromium, oxide of copper, baryta, lithia, 
sulphur, &c. 

The quantitative proportions of the essential elements 
vary considerably in different rocks, but this variation is 
almost as great between different kinds of the same rock 
as between the different rocks themselves ; and no igneous 
rock is of so invariable or marked a chemical character as 
to be distinguishable from the rest by it alone. 

Taking the whole range of the igneous rocks, the 
average values of their chemical constituents may be 
stated somewhat as follows : 

Extreme actual values. Ideal average. 

45 
15 
10 
6 
5 
4 
4 
2 

Where the extreme values, as above given, are found 
to be exceeded on the one side or the other, the excess or 
deficiency appears invariably to have been the result of 
change, decomposition, or some similar process subsequent 
to the formation of the rock, which, therefore, is no 
longer in its original state. 

We have already indicated the division of the igneous 
rocks, in respect of their chemical composition, into two 
principal groups. 

1. Poor in silica, or basic. 

2. Rich in silica, or acidic igneous rocks. 

The distinction between these two groups is deserving 
of considerable attention, for they also differ to some 
extent both mineralogically and geologically, although 
they cannot be very rigidly separated from each other ; 
and certain rocks of each group vary so greatly in their 
composition as actually to graduate into the opposite 
group. 

The following proportions may be stated as an approxi- 
mate average of the analysis for the two groups : 



Silica 
Alumina 
Peroxide a 
Liine 
Magnesia 
Potash 
Soda 
Water 


mdP 


rotox 


de oi 


Iron 


5080 
1025 
125 
015 
012 
010 
7 
5 



364 PROCESSES OF ROCK FORMATION : 

Basic. Acidic 

Silica . . * '" ~. 4560 55-80 

Alumina 1025 1015 

Iron (Peroxide or Protoxide) . 1 25 1 15 

Lime J , .'. ! . . . ' , . 115 08 

Magnesia 112 4 

Potash 19 111 

Soda 17 28 

Water 04 06 

These two groups nearly correspond with the pyroxenic 
and trachytic groups of Bunsen, for which he calculated 
certain ideal or normal average values of their elementary 
constituents.* (See Poggend. Ann. 1851, vol. Ixxxiii.) 

Without, therefore," being able to fix any very precise 
standard, the distinguishing feature of the basic rocks is, 
that they contain less silica, more alumina, iron, lime, and 
magnesia, and less alkali than the acidic rocks. Within 
the limits of each group we find no constant differences 
of chemical composition between the several species. 
These only differ in their mineral development, their 
texture, or the mode and accidents of their occurrence in 
nature. 

We may, therefore, say in general terms that all 
igneous rocks consist of one or other of two compounds 
normally differing in the proportions of their elementary 
constituents, but that several intermediate gradations 
exist between the two extremes. Each of these two 
compounds has produced many different species and mo- 
difications of rock which have received different names. 
The differences are partly those of texture, partly of 
mineral composition. The first may in most cases be very 
simply accounted for by the particular circumstances of 

* Bunsen's values of the different elements were as follows : 

Pyroxenic. Trachytic. 

Silica 48-47 76-67 

Alumina and Protoxide of Iron 30-16 14-23 

Lime ; . . . . 11-87 1-44 

Magnesia 6-89 0-28 

Soda ... . . . 1-96 3-20 

Potash 0-65 4-18 



100-00 100-00 



IGNEOUS ROCKS. 365 

cooling. The quicker the cooling process, the more com- 
pact or even vitreous the product would be; and the 
slower the process, the more crystalline and coarse- 
grained would the rock become. Inequality in the crys- 
tallising power of the different ingredients would give a 
porphyritic texture ; parallel arrangement of certain of 
the ingredients would give a slaty or schistose texture ; 
development of gases during the cooling would give a 
vesicular or slag-like texture. 

The differences of mineral composition are not great. 
In most cases the elementary substances are the same ; 
and the differences of proportion in which they are com- 
bined are so small as to appear unimportant. We are 
unable satisfactorily to explain in any particular case why, 
with differences of composition so trifling, one particular 
species of felspar, of hornblende or pyroxene, or of mica 
was produced rather than another, or why, under ap- 
parently similar conditions in another rock, other mi- 
nerals, such as nepheline, leucite, talc, chlorite, &c., were 
formed in their stead. A part only of these differences 
can be traced to have any distinct relation to the quan- 
titative proportions of the chemical composition of the 
whole rock. Other differences consist in the presence of 
various accessory minerals. These we may presume to 
represent a surplus or residuum of certain elementary 
substances remaining uncombined after the crystallisation 
of the essential mineral ingredients. Many accessory 
minerals are, however, evidently the result of later pro- 
cesses of transmutation. 

If we disregard the specific but minor differences be- 
tween those similar minerals, which, to a certain extent, 
occur as substitutes for each other in rocks, we find a 
certain correspondence in the mineralogical with the che- 
mical phenomena, and that, speaking generally, there are 
two principal kinds of rock essentially differing from each 
other in the aggregate of their mineral composition, 
if only in their normal states of development one a 
basic, and the other an acidic compound. These are again 
subdivided, according to their texture and recognisable 
mineral differences, into rocks of several species, as indi- 
cated in the following tabular statement. 



PROCESSES OF KOCK FORMATION: 



Granular 


Porphyritic 


Compact 


Vitreous, vesicu- 
lar, or amygda- 
loidal 


Slaty-schistose 
(chiefly meta- 
morphic) 


^ /Granite 
"1$ Syenitic- 
^ j granite 
.0 ] Protogine 
^ Trachyte 
^ V(Greisen) 


Granitic- 
porphyry 
Quartz- 
porphyry 
Trachyte- 
porphyry 


Felsite rock 
Petrosilex 


Pitchstone 
Pearlstone 
Obsidian 
Pumice-stone 


Granulite 
Gneiss 
Protogine- 
gneiss 
Felsite-schist 
(Mica-schist) 


4 
f. 


^Syenite 
Diorite 
Diabase 
Timacite 
Dolerite 
Nepheline- 
dolerite 
Gabbro 
Miascite 
^Mica-trap 


Hornblende- 
porphyry 
Mica-por- 
phyry 
Porphyrite 
Aphanite- 
porphyry 
Melaphyre 


Melaphyre 
Aphanite 
Basalt 


Vesicular 
rocks and 
amygdaloids 


Hornblende- 
schists 
Chlorite-schist 
Talcose schist 



As already stated, the mineral differences in the ig- 
neous rocks do not appear to have been all original, 
but to have been partly produced at a later period by 
process of transmutation. In individual cases this has 
been very well shown to be the fact by Bischof and 
Rose, although both of those distinguished men may, per- 
haps, have gone too far in their hypotheses on this sub- 
ject. The extent to which such transmutations have 
taken place is not yet established by proof, and we 
may say generally that it is impossible to be too cau- 
tious in admitting the process of transmutation as a suffi- 
cient explanation of differences between rocks, unless 
we are willing to be content with mere convenient hypo- 
theses. 

We have already observed that the causes are not yet 
satisfactorily ascertained why, from compounds chemically 
very similar, in one rock orthoclase has resulted, in others 
sanidine, oligoclase, labradorite, anorthite, &c. ; in one 
rock a hornblende, in another a pyroxene. 

The exact causes of these phenomena can never be 
ascertained with certainty. One cause, however, of dif- 
ferent forms of mineral development may be well con- 
ceived, viz. the different depths at which cooling and 
solidification have taken place in rock masses. It cannot 



IGXEOUS ROCKS. 367 

be doubted that the conditions under which substances 
have combined to form minerals were very different at a 
depth of 10,000 feet from those which prevailed at a 
depth of 10 or 100 feet only from the surface. In the 
former case the masses have been subjected to far higher 
pressure were shut out from the atmosphere they were 
probably exposed in some degree to the action of water, 
but their cooling must, in masses of equal bulk, have 
been on the average a much slower process than would 
have obtained near the surface. Again, not only the 
depth of the formation, but the geological period of the 
earth's development may have had considerable influence 
in determining the character of minerals. For if the 
theory is correct that the earth has cooled into a solid 
from a previous molten state, its average temperature in 
former periods, even at the surface, must have been 
higher, and the atmosphere more dense and heavy than 
at present. Each cooling process under such circum- 
stances would be slower, and would take place under a 
different degree of pressure than now. Thus we have 
one recognised general cause for the differences we ob- 
serve ; but the definite proof of what its precise effects 
have been under different circumstances is wanting. 

The cause for a division of the igneous rocks into those 
poor in silica and rich in silica remains a great problem 
for solution. A priori we should expect to find all 
igneous rocks of the same composition. Bunsen's theory 
of the existence of two separate volcanic furnaces in the 
interior of the earth is a mere hypothesis, which, no 
doubt, might, if it were true, suffice to explain the exist- 
ing differences, but which in itself is very improbable. 
Such furnaces, if they existed at all, must have been in 
existence through all geological time ; in almost every 
part of the globe they must have been placed side by 
side or one above the other, and yet have remained dis- 
tinct and unmixed. No circumstance, unless it be the 
very difference which we are endeavouring to explain, 
speaks for such an assumption. Even if the cooling and 
solidifying of the fluid mass of the globe should have pro- 
ceeded contemporaneously equally from the centre and 
surface towards a middle plane, as Bunsen supposes, so 
that at last only an intermediate stratum of fluid matter 



368 PROCESSES OF ROCK FORMATION : 

will remain between the two, the existence of separate 
basic and acidic basins of lava will not by this assume 
greater probability. For the present we must confess 
that the cause of the differences between these two chief 
groups of igneous rocks has not yet been satisfactorily 
explained. 

It has been very ingeniously suggested that a cause 
might be sought in the different specific gravity of the 
several rock masses, starting with the assumption that in 
the former molten state of the earth the ingredients must 
have arranged themselves in some measure according to 
their specific gravity ; so that the heaviest substances 
would be accumulated towards the centre, and the lighter 
towards the surface. If the cooling process began with 
the outside of the globe proceeding inwards, then it 
follows that the specifically lighter bodies would first 
attain the solid state, and these we actually find to be 
richest in silica ; and that the heavier bodies, which are 
at the same time the most basic, would only cool at a 
later period. This law, it was considered, must prevail 
alike in an incrustation formed under quiet circum- 
stances, as in the case of eruptive rocks necessarily emer- 
ging from a great and ever increasing depth ; so that the 
oldest would be the lightest and most acidic ; the recent 
the heaviest and most basic. This theory, which Petz- 
bold (in his Geologie, 1840) pushed to the utmost ex- 
treme, i. e. to the formation of mineral veins, has been 
lately attempted to be applied in a narrower sense by 
Von Eichthofen (Greol. Beschreib. von Sud-Tyrol, 1861, 
p. 308). It evidently has a great appearance of theo- 
retical probability in its favour. But when we come to 
test this theory by comparison with ascertained facts, we 
at once find it untenable, at least in part, and undoubtedly 
altogether insufficient satisfactorily to explain those facts. 
Every geological age has produced acidic as well as 
basic, specifically light and specifically heavy, igneous 
rocks. Where syenite and granite occur together, it is 
even most usually the case that the basic syenite is older 
than the acidic granite. The basic porphyries in the 
Thuringian Forest and the Erzgebirge are on the 
average older than the acidic quartz-porphyries which 
belong to the same great period. The trachyte-por- 



IGNEOUS ROCKS. 369 

phyries belong to the most acidic and yet frequently to 
the most recent eruptive rocks. According to von 
Richthofen's own investigations, they are, on an average, 
of more recent formation than the trachytes, which con- 
tain less silica and are also somewhat heavier. Therefore, 
von Richthofen himself, to support his theory, was com- 
pelled to have recourse to various hypotheses, such as a 
second fusion and new eruption of old igneous rocks, &c., 
which in themselves are neither probable nor sufficient to 
solve all the difficulties of the case. We have yet to seek 
the true solution of many important problems relating to 
this subject. Nevertheless, we are not of opinion that the 
theory of an arrangement of substances according to their 
specific gravity should be disregarded as entirely un- 
worthy of serious attention. Specific gravity may, and 
probably has had, a certain influence in the first arrange- 
ment of rock masses ; and if we are unable now to trace 
a consistent arrangement deducible from the laws of 
specific gravity, it may be only because those traces have 
to a great extent been subsequently effaced by other cir- 
cumstances which we have not yet discovered. A primary 
crust formed by cooling and the first sedimentary deposits, 
resulting from the decay of that first crust, may well have 
been pre-eminently rich in silica ; more especially if at 
the time of those sedimentary deposits animal life had not 
begun to act on the calcareous waters, and so cause a 
redeposit of the dissolved lime in large masses. If this 
primary portion of the earth's crust should at a later date 
have been subjected to a second process of fusion under 
high pressure, at a considerable depth, it may have 
become partially eruptive, and have produced recent 
rocks very rich in silica and of very uniform chemical 
composition. We may, in fact, reasoning from analogy 
to the meteoric stones, which represent to us the small 
planetary bodies of our solar system, believe the aggre- 
gate of the earth's mass to be far more strongly basic 
than that part of it which is open to our observation. 

Taking into account composition, on the one hand, and 
geological character, on the other, we come to distinguish 
four great groups of igneous rocks, which groups are, 
however, not divided from each other by exact bounda- 
ries. Each may be characterised by some typical rock ; 

B B 



370 PKOCESSES OF ROCK FORMATION : 

and each may be also connected with the other groups by 
means of other rocks of intermediate character. We may 
represent these groups somewhat as follows : 



BASIC -f ^ mmc : Basalt ") Diabase, Porphyrite, 

' \ Plutonic : Diorite J Melaphyre 



or : 



ACIDIC [ ^kamc : Trachyte 1 Trachyte-porphyry 
' I Plutonic : Granite J Quartz-porphyry 

Vn , .,. {Basic : Basalt \Trachydolerite. Andesite, 
C ' \ Acidic : Trachyte JPorphyrite 

-r^ {Basic : Diorite | ., 

PLUTONIC . . Senite 



A ^. Q . Granite 



| ., 
j Syenit 



We must not omit to remark that some considerations 
entitled to attention have been started against the igneous 
character of certain of the rocks so named, and chiefly 
those which contain quartz. 

Granite is the principal representative of these rocks. 
In the case of this rock, so universally spread over the 
surface of the globe, it has been objected that, look- 
ing to the mode in which its essential ingredients, fel- 
spar, quartz, and mica are joined together, and fitted 
one into the other, those minerals could not have been 
formed in the order of their respective degrees of rapidity 
of solidification from a state of fusion, i. e. first the 
quartz, then the felspar, and last the mica ; but, on the 
contrary, that it very often appears distinctly that the 
quartz, which is the most difficult of fusion, has been 
formed the last. It has been further objected that in 
granite, as well as in many other, even in certain basic 
igneous rocks, there sometimes occur accessory minerals 
whose formation by igneous means can scarcely be con- 
ceived as possible, or at least is contradicted by all 
experience. For instance, pyrites, apatite, pyrochlore, 
carbonate of lime, carbonate of magnesia, protocarbonate 
of iron, &c. These are found side by side with silicates, 
and yet without forming chemical combinations with the 
latter. Finally, it has been objected that many so-called 
igneous rocks contain some water, and according to the 
analyses of Delesse, even small quantities of nitrogen. 
(Ann. des. Mines, 1860, vol. xviii.) 

Now, as regards the first objection the solidification of 



IGNEOUS ROCKS. 371 

the quartz subsequently to the felspar Durocher has long 
since shown (Gompt. rend. 1845, p. 1275), that in fusing 
the compact rock petrosilex, whose composition is often 
precisely the same as that of granite, the quartz which it 
contains being associated with the other ingredients of 
the rock, is quite as readily fusible as felspar alone ; and 
hence we may conclude that upon the cooling of such a 
mass the quartz would not necessarily separate itself from 
the rest of the compound by solidifying sooner than the 
felspar. If this be so, in the case of a granitic mass it 
might depend on some circumstance, which for want of a 
better term we may call accident, whether the quartz 
or the felspar should first happen to complete the pro- 
cess of its crystallisation, and whichever of those two 
minerals first crystallised would necessarily determine 
the form of the other. Now the felspar in granite ap- 
pears to have been the first to crystallise, and has deter- 
mined the form of the quartz in many cases. Bunsen has 
lately thrown much light on this question (vide Zeitsch. d. 
geol. Ges. 1861, p. 61); he has shown that the melting 
and solidifying points of a mineral, when taken singly, by 
no means determine those of an intimate compound or 
alloy of such mineral with other mineral or minerals. In 
a letter to Streng, which appeared in the Berggeist 
(1862, p. 1), Bunsen, in illustration of the same law, 
adduces instances of aqueous solutions, where heat is ne- 
cessary to the solution. The so-called PattinsorCs pro- 
cess is the result of a similar experience. It is found that 
pure lead crystallises sooner than lead containing a pro- 
portion of silver ; and accordingly when the liquid mass 
of mixed lead and silver is subjected to a process of slow 
cooling, the pure lead congeals first, leaving the richer 
metal still in a fluid state (termed ( mother water'). More- 
over, high pressure and water (chemically combined) may 
have exercised many important modifying influences upon 
the process of the formation of the granitic rocks. 

The second suggestion referring to the presence of cer- 
tain minerals as accessory ingredients in so-called igneous 
rocks which appear incompatible with their igneous origin, 
loses much of its force from our likewise finding some of 
the same minerals in genuine lavas, whose origin is un- 
doubted. Moreover, those minerals or substances may 

BB 2 



372 PEOCESSES OF ROCK FORMATION : 

not have been actually present in the rocks in question at 
the period of their first formation, but have originated in 
them at a later date. As to the water contained in rocks, 
Scheerer has clearly proved that water forms a basic in- 
gredient of many minerals (e.g. many kinds of mica), 
entering into combination with silica and other acids in 
precisely the same way as any other basic oxide. Dau- 
bree has established the same fact synthetically, showing 
that under great pressure at a high degree of temperature, 
water may be made chemically to combine with mineral 
matter. Whether the very small quantity of nitrogen 
contained in many igneous rocks was there originally, or 
whether it only insinuated itself into them at a later 
period, may, for the present, remain an open question ; all 
minor difficulties like this will probably find a satis- 
factory solution in time. On the other hand, as regards 
the carbonates of lime, magnesia, and iron contained in 
igneous rocks, they appear to be invariably the result of 
change or transmutation subsequent to the formation of 
the rock. Hence we never find them in very recent lavas, 
but only in those igneous rocks which have been long 
and continuously exposed to the action of chemical in- 
fluences, calculated to bring forth those minerals, and 
therefore we find them more frequently in the plutonic 
than the volcanic rocks. Pyrites, magnetic pyrites, chlo- 
rite, and talc, all likewise appear to have been the result 
of such transmutations, even if we cannot as yet satis- 
factorily so explain every single case of the occurrence 
of a particular mineral. These considerations prevent us 
from attaching much weight to the objections raised to 
the igneous origin of granite an origin which on other 
grounds appears so conclusively established. 

The differences between the volanic and plutonic rocks 
of both principal groups, the basic and acidic (although 
smaller and more filled up by transition states than 
those between the two groups themselves), deserve a 
full share of our attention, and require some explana- 
tion. We have already more than once adverted to one 
general cause of difference, namely, the unequal condi- 
tions, under which the cooling and solidification first took 
place, whether under simple or multiplied atmospheric 
pressure ; and whether on the surface of the globe, or in 
a closed space, where water probably had access. 



IGNEOUS ROCKS. 



373 



Besides these original causes of difference, there are also 
the many changes which appear to have taken place in 
the state as well as composition of all rocks, subsequently 
to their first formation, chiefly no doubt under the in- 
fluence of water and gas penetrating and permeating 
them. 

In the present state of science it is impossible every- 
where separately to specify and define the results of all 
these different causes, yet we will attempt by contrasting 
the characteristic attributes of the two principal groups 
to present some general views applicable to the subject. 

The original differences may shortly be stated as fol- 
lows : 



In Volcanic Rocks. 

Prevalent compact, porphy- 
ritic, vesicular, or vitreous 
states. Seldom or never slaty 
or schistose texture. 

Small content of water. 

Seldom crystallised quartz. 

Frequent tufa formations. 



In Plutonic Hocks. 

Prevalent crystalline -granular and 
porphyritic, sometimes also schistose 
or slaty texture; seldom vitreous or 
vesicular. 

Greater content of water. 

More frequently crystals of quartz. 

Seldom tufa formations. 



The differences occasioned by gradual metamorphosis 
are as follows : 

In Volcanic Rocks. In Plutonic Rocks. 

There is little or no change. The formation of amygdaloids, by 

the filling up of previously existing 
vesicular cavities with newly-formed 
minerals. 

The new formation or transforma- 
tion of certain minerals in the in- 
terior of the mass, e.g. pyrites, car- 
bonates, zeolites, apatite, chlorite, 
talc, serpentine, &c. The absorption 
of more water. Decomposed wacke- 
nitic states; possibly even many 
formations of quartz. 

To sum up these observations : It appears that in the 
present state of science we cannot but regard all the so- 
called igneous rocks as parts of the earth's interior mass, 
thrust out whilst in a state of fusion, without being able 
as yet satisfactorily to explain their division into the two 



374 PROCESSES OF KOCK FORMATION : 

principal groups of acidic and basic composition respec- 
tively, the minor differences inside of these groups being 
capable of explanation by the different circumstances 
under which the several rocks attained the solid state or 
by subsequent process of their transmutation. 

In addition to the works cited in the text we will here 
only notice the following : 

Deksse, on the origin of igneous rocks, in Compt. rend. 1859, 
vol. xlviii. p. 955 ; v. L. u. Br. Jahrb. 1859, p. 459 ; and Ann. 
des Mines, 1858, vol. xv. p. 459. Delesse distinguishes between 
Igneous rocks (trachyte, dolerite), Pseudo-Igneous rocks 
(trap), and Non-Igneous rocks (granite, diorite, &c.). If 
we wish for extreme precision of nomenclature, the term 
Igneous is altogether inappropriate, even for the volcanic 
rocks, which have but consolidated from a state of liquid 
fusion, without any fire or burning in the ordinary accepta- 
tion of the word fire. Hence in Germany the Igneous rocks 
are termed Eruptive rocks. One name is as good as another 
for practical purposes, if we do not seek to attach theory 
too closely to nomenclature. 

Daubree, Sur le Metamorphisme et sur la Formation des Roches 
Cristallines, 1860. 

Scheerer, iiber den Astrophyllit und sein Verhaltniss zu Augit 
und Glimmer und Zirconsyenit nebst Bemerkungen iiber 
die plutonische Entstehung solcher Gebilde, 1864. 

See also Cotta's Geologische Fragen, 1858. The argument 
against the igneous origin of granite which has been built on 
the score of the specific gravity of the quartz falls to the 
ground if we believe that it became solid under high pressure. 



SEDIMENTARY ROCKS. 

The general character of the processes by which these 
rocks were formed is well known and evident. They are 
deposits of fallen substances, chiefly precipitated from 
water a small part from the atmosphere. This, their 
origin, is proved in a variety of ways, by their composi- 
tion, their stratification and bedding, and the fossils which 
they enclose. 

A few words as to their composition may not be out of 
place here. 

If the views now prevalent respecting the earth's history- 
are correct, the igneous rocks must be regarded as the 



SEDIMENTARY ROCKS. 375 

most original, or rather the only original formations. 
Should it appear that any part of the first crust produced 
by the original cooling of the earth's surface remains un- 
disturbed at the present day, it will properly belong to 
the igneous rocks, although not like the other igneous 
rocks, eruptive. If we take all the igneous rocks together, 
we have products of the eruptions of all geological pe- 
riods. To these products we must, therefore, chiefly look 
for information as to the nature of the substances con- 
tained in the interior earth's mass. They may represent 
a part only of that mass, but they constitute our only 
evidence on the subject. The nucleus of the earth may 
possibly be differently composed, but we possess no means 
of investigating it. 

In the aggregate composition of the sedimentary rocks, 
which we assume to be but the product of decomposition, 
re-deposition, and transmutation of the original and first 
consolidated igneous rocks, we should expect to find the 
same ingredients as in the igneous rocks, and in somewhat 
similar proportions. Therefore we should look for silica 
as the predominant ingredient, and alumina, oxides of 
iron, lime, magnesia, potash, and soda in smaller quanti- 
ties. We do, indeed, find these to constitute the sub- 
stance of the stratified rocks (although not grouped in 
the same manner as in the igneous rocks). We likewise 
find other ingredients such as compounds of carbon, sul- 
phur, and chlorine ; but these we infer have been derived 
from the atmosphere or from water. It is doubtless very 
difficult to form a sound opinion, whether in point of fact, 
the quantitative proportions of the ingredients we have 
first named are in the aggregate about the same in the 
sedimentary as in the igneous rocks, since the combina- 
tions are for the most part very different in the two classes. 
In the sedimentary rocks the lime and magnesia have 
vmited with carbonic acid to form the limestones and 
dolomites, or with sulphuric acid to form gypsum and 
anhydrite ; silica has produced quartzite rocks and the 
sandstones ; alumina has combined with silica to form 
the argillaceous rocks; oxides of iron, the ironstones 
(iron is also much disseminated in other rocks); potash 
and soda have become very much distributed amongst 
many kinds of sedimentary rock ; soda, again, has united 



376 PKOCESSES OF EOCK FORMATION : 

with muriatic acid to form rock-salt ; carbon (concentrated 
by process of vegetation) has formed coal-beds. 

At a cursory glance it might appear as if the sedi- 
mentary rocks in the aggregate contained more lime and 
less potash than the igneous. We must, however, re- 
member that some lime is contained in almost all igneous 
rocks (especially the basic rocks), but by no means in all 
sedimentary rocks ; again, that the sulphuric acid and 
water make up a very considerable part of the bulk of 
the limestones, dolomites, and gypsums ; which bulk we 
may moreover easily be led to overrate as they are apt 
to stand out very conspicuously and prominently amongst 
the other sedimentary rocks in separate and excep- 
tionally compact masses. Taking all these circumstances 
into account we should probably find that the proportion 
of lime in the aggregate of the stratified rocks does not 
essentially differ from that in the aggregate of the igneous 
rocks. As regards the potash we must recollect that its 
quantity in the igneous rocks only reaches about 4 per 
cent, as an approximate average, that the greater part of 
the sedimentary rocks contain some potash, and several 
a very considerable quantity. Great quantities of soda 
have been converted into rock-salt. We have, therefore, 
no sufficient reason to doubt that the aggregate ingre- 
dients of the igneous and the sedimentary rocks are 
equally balanced. 

In the case of all sandstones, stratified conglomerates, 
tuff formations, compact and slaty argillaceous rocks, as 
well as the greater part of the marls, limestones, dolo- 
mites, and coals, their sedimentary origin is so appa- 
rent that nobody will doubt it. The matter is less clear 
in the case of many granular limestones and dolomites, 
also in that of the massive accumulations of rock-salt and 
gypsum, although the sedimentary origin of these latter 
is now generally admitted. It is most difficult to dis- 
tinguish the sedimentary from the igneous rocks in those 
cases where the two are found interlying each other in 
parallel beds as sometimes happens, the igneous perhaps 
indistinctly composite or even somewhat decomposed. 

Whilst we thus find no difficulty in pronouncing on the 
origin of the sedimentary rocks in general, it is somewhat 
difficult to determine what rocks we should reckon as 



SEDIMENTARY ROCKS. 377 

sedimentary, and in what cases we should apply the terra 
* metamorphic.' 

The expression ' metamorphic ' will best serve a useful 
purpose of distinction if it be reserved for cases where a 
rock originally sedimentary (according to our previous 
definition) is so essentially changed in its mineral cha- 
racter as not to be capable of recognition without the 
evidence of collateral circumstances to identify it with the 
original formation. From the nature of the case, how- 
ever, no distinct division between the sedimentary and the 
metamorphic rocks is possible ; on the contrary, gradual 
transitions take place from one to the other, and the ex- 
tremes alone are distinctly different in their character. 

There remains much for investigation as to the parti- 
cular circumstances under which the several kinds of sedi- 
mentary rock came to be deposited. 

\Ve cannot lay down any general law applicable to all 
sedimentary rocks as to the conditions under which their 
first deposit took place. The case of each rock has to be 
separately considered with reference to its bedding, and 
the organic remains which it contains. The most that we 
can say as a general proposition is, that many of these 
rocks have been deposited by the sea some on the coasts, 
some at a great distance from the shore ; others have been 
deposited in freshwater lakes by means of rivers or springs. 
The greater part consist of matter washed together by 
floods ; some consist of the ejectamenta of volcanoes ; 
some are crystalline precipitates, and some are the result 
of processes of animal and vegetable life. 

Nor can we in general terms describe the mechanical 
forces which have acted on the materials of the sedi- 
mentary rocks to fit them for union, the mode of that 
union, the separation or combination of the chemical 
ingredients, the nature of the substances which have been 
introduced or become changed subsequently to the first 
deposit, the alterations of level which have taken place 
in the beds of those rocks by depression or upheaval, 
&c. All these are of great moment to be determined, 
but they can only be subjects of separate consideration in 
each individual case. 

The oldest rocks which are capable of being recognised 
at the present day as distinctly sedimentary, are those of 



378 PROCESSES OF ROCK FORMATION I 

the transition period. Now as these rocks still contain a 
considerable number and variety of organic remains, it is 
reasonable to conclude that there have been many of yet 
more ancient date, for, according to the igneous theory of 
the earth's structure there must necessarily have existed 
a long period of time in which deposits took place before 
any organic remains existed. These oldest deposits would 
be the lowest sedimentary formations, and would contain 
few or no fossil remains. It is probable that they have 
been changed into, and now form the principal bulk of 
the metamorphic schists. If we would speculate on their 
former probable structure, we should expect their compo- 
sition to have been very uniform, because at the time of 
their deposit there were fewer causes for difference in 
rock formation than in later periods ; many of such 
causes having arisen subsequently, such for instance as 
organic life, the origin of many calcareous, and all the 
carboniferous strata. Reasoning backwards, if we believe 
the crystalline schists to have chiefly sprung from the 
oldest sedimentary rocks, we may thus account for their 
very rarely enclosing calcareous or carboniferous beds 
(limestone and graphite). That the composition of these 
crystalline schists should much resemble that of the first 
igneous rocks, would seem to be but a natural consequence 
of their transmutation from the earliest sedimentary rocks, 
which themselves were the products of the disintegration 
of those first igneous rocks. But these speculations should 
be indulged in with caution, as they may easily lead us 
too far into the regions of unfounded hypothesis. 

METAMORPHIC CRYSTALLINE SCHISTS. 

Notwithstanding what we have had occasion to remark 
in describing the sedimentary rocks, the true interpreta- 
tion of the crystalline schists remains one of the most 
difficult problems for the geologist, since the process of 
their formation can only be subject of theory, and not of 
direct observation. 

Various theories as to the nature of their origin have 
been advanced. They have .been taken for the original 
deposits of a so-called antediluvian age ; for the first cooled 
igneous products of the earth ; a part for rocks of eruptive 



METAMORPHIC SCHISTS. 379 

character ; and finally for sedimentary rocks very greatly 
changed or transmuted. These different views have been 
put forward at different times, have been more or less 
accepted, but all except the last have been very generally 
abandoned. 

Nobody now holds that the crystalline schists were 
deposited in their present state and condition. A few at 
most may have been formed by the first cooling of the 
earth's crust perhaps some gneiss districts, if any such 
can be found entirely free from subordinate interlying 
beds. It is improbable that such origin can ever be satis- 
factorily proved, and it remains for the present at best 
an hypothesis which is possible for certain cases. Some 
gneiss certainly appears to be of igneous (eruptive) origin, 
but a very large proportion of the known gneiss forma- 
tions admit of no such explanation, nor is it applicable 
to any of the other crystalline schists. From a geological 
point of view we shall therefore do well to consider the 
eruptive gneiss as a schistose variety of granite, and 
every other (for the present at least) as metamorphic. 
Hence, according to the present state of our scientific 
knowledge, the only explanation left for by far the greater 
part of the crystalline slates is that of transmutation 
from sedimentary formations. 

The following are some of the principal reasons which 
appear clearly to speak for such transmutation, without, 
however, giving us certain information as to the manner 
of the process : 

1. Those rocks the traces of whose sedimentary origin 
are evident and distinct, present us with numerous series 
of transitions tending towards or rendering possible further 
transitions into crystalline schist, or corresponding with 
the subordinate beds which are found interlying those 
schists. We will give a few instances of such series of 
transmutation : 

(a) Clay -mud successively passes into (or becomes) 
argillaceous shale, clay-slate, argillaceous mica-schist, 
and mica-schist. If this be so we should expect in 
the final products of this series of transmutations to 
find indications of the special composition of the dif- 
ferent original clays influencing the character of each 
rock, which accordingly should vary with the varying 



380 PROCESSES OF ROCK FORMATION: 

quantities of sand, lime, magnesia, potash, or soda con- 
tained in the original clay. And to such differences of 
original composition we do in fact attribute the different 
varieties of mica-schist, or the formation in its stead of 
gneiss, hornblende-schist, chlorite-schist, or talc-schist 
(although the special character of the two latter is pro- 
bably in some measure owing to the later accession of 
solutions of magnesia). 

(#) Sand passes into (or becomes) sandstone, quartz- 
ite, quartz-schist, or itacolumite, according to the 
character of the substances originally mixed with the 
sand, or which have subsequently come to it. A mica- 
schist rich in quartz, or a gneiss, might also result from 
the transmutation of a sandstone having a copious com- 
bining medium. 

(c) Calcareous mud, consisting of microscopically 
small shells, passes into (or has actually become) chalk ; 
chalk (probably by means of pressure) has turned 
to compact limestone. Chalk or compact limestone 
under pressure, by means of a high degree of tem- 
perature, may have been transmuted into granular lime- 
stone, beds of which frequently occur in subordinate 
layers between the strata of crystalline schists. 

(c?) Browncoal, coal, anthracite, and graphite have 
without doubt resulted from peat or other vegetable 
accumulations. Anthracite and graphite we again find 
as subordinate formations imbedded between strata of 
crystalline schists. 

(e) Hydrated oxide of iron forms a deposit in the 
form of bog-ore or brown hematite, and these under 
the pressure of thickly overlying masses appear to have 
parted with their water, and become converted into red 
iron-ore, or red hematite. Further, by the absorption 
of one part of oxygen, red iron-ore is converted into 
magnetic iron-ore. The latter is found in subordinate 
layers between beds of crystalline schists. But in each 
of these cases the transmutations are sometimes found 
to have been reversed, and other processes have taken 
place which have somewhat complicated the actual 
phenomena. 

2. The several kinds of crystalline schist and their 
different varieties are found imbedded in manifold parallel 



METAMORPHIC SCHISTS. 381 

alternating layers or strata. Between these lie subordi- 
nate layers of granular limestone, dolomite, quartzite, 
ironstone, graphite, &c., and the whole series are found 
stratified in a parallel direction. This alternate bedding 
and imbedding correspond exactly with that of the sedi- 
mentary rocks their state only is changed, being usually 
crystalline. The bedding and stratification of the crys- 
talline schists therefore furnishes a second and most im- 
portant argument for their metamorphic origin ; in no 
other way can the existing phenomena be accounted for. 

3. The usual or normal bedding of the crystalline 
schists is lower than that of all sedimentary rocks, and 
complete gradual transitions between the two are fre- 
quently to be observed. These outward indicia alone are 
strong evidences of metamorphic origin. 

4. Finally, we may bring certain more rare or ex- 
ceptional phenomena in proof of the theory of transmu- 
tation, e.g. the occurrence in strata of crystalline schist 
of beds containing certain still recognisable fossils ; as for 
instance the limestone-slate with remains of belemnites 
between the mica-schist and gneiss of the Alps, at the 
Furca and Pass of Nufenen. At the last-named locality 
more recent formations are also found exceptionally very 
much changed, but not entirely transmuted. 

Taking all these facts together they appear to us to 
furnish as complete a chain of indirect evidence in favour 
of the transmutation of a very large proportion of the 
crystalline schists as we could well expect to find where 
from the nature of the case direct observation is un- 
attainable. 

The causes and manner of the transmutation, however, 
constitute a different question. 

The first theory of geologists upon this matter was that 
the crystalline schists had been formed out of the sedi- 
mentary by the operation of great eruptive masses of 
igneous rocks thrusting themselves through, over, and by 
the side of the sedimentary rocks therefore by the effect 
of contact ; and it was also supposed that the felspar of the 
gneiss was only forced into it from granitic compounds. 
The frequent occurrence of granite in the immediate 
neighbourhood of gneiss, the fact that granite districts 
are frequently entirely surrounded by gneiss, which latter 



382 PROCESSES OF ROCK FORMATION : 

gradually merges into mica-schist towards its external 
boundary (as for instance, in many parts of the Erzge- 
birge) ; all these and like phenomena might no doubt 
be cited in favour of such an hypothesis. But on the 
other hand, no possible explanation could be afforded on 
this assumption for the uniform distribution of the felspar 
in the gneiss, nor for the extent of the supposed effect 
of the contact without a regular diminution of force cor- 
responding with the distance from the transforming cause. 
Very frequently the observable mass of eruptive rock 
(which according to the theory should be the cause of 
the transmutation) bears no adequate proportion to the 
extent of the crystalline schist (which has become trans- 
muted). Many large districts of crystalline schist are, 
moreover, entirely free from granitic or other eruptive 
intrusions ; and it would, to say the least, be hazardous in 
such cases always to presume the existence of a substratum 
of granite which had failed to penetrate to the surface. 
Again, many considerable granite districts are not sur- 
rounded by gneiss or other crystalline schists, but on the 
contrary are immediately in contact with distinctly sedi- 
mentary rocks, which latter have remained almost entirely 
unchanged by the contact, or at all events are not changed 
into crystalline schists, although their bedding shows 
clearly enough that they have been actually broken 
through by the granite. The Hartz and Saxon Yoigt- 
land afford remarkable instances of this kind. Thus we 
find clay-slate formations of different ages broken through 
by great masses of granite ; at the margin of the granite, 
however, we find no trace of gneiss or mica-schist forma- 
tions, but only the ordinary clay-slate changed for a 
relatively small distance into horns tone, nodular schist 
(Knotenschiefer), or chiastolite-schist changes which no 
doubt have been caused by contact with the granite, 
but which bear no resemblance to gneiss-formations, and 
are probably the consequence more of a hydroplutonic 
operation than of the high temperature of the granite 
alone. 

We are aware that Credner (in v. L. u. Br. Jahrb. 
1849, p. 8) has described an occurrence at Glasbach on 
the Schwarza, in the Thuringian Forest, where it really 
appears as if the clay-slate, broken through by a very 



METAMORPHIC SCHISTS. 383 

considerable dyke of granite, has been transmuted into 
gneiss for some short distance from the granite. Under 
special circumstances, and if we find the clay-slate to 
contain the same elements as the gneiss, we may well 
admit the possibility of such an effect of the contact of 
granite without our being authorised therefore to con- 
clude that all gneiss has arisen from the same or similar 
transmuting causes. We should rather regard such an 
instance as proving that in particular cases special causes 
have been competent to supply those more universal con- 
ditions and processes of transmutation by which the 
greater part of gneiss rocks have been formed ; just as in 
the neighbourhood of basaltic rocks and porphyries ex- 
ceptional formations of anthracite have taken place. 

From all these considerations we gather that no effect 
which could be produced by the contact of eruptive 
igneous rocks would be sufficient to have caused the 
formation of the great mass of the crystalline schists, but 
that we should rather look for causes much more general 
in their operation. These are most probably no other 
than pressure and heat. We accordingly hold that not 
only the crystalline schists but also the subordinate masses 
imbedded in them are nothing more than the latest result 
of that very general process of transmutation which all 
sedimentary deposits have undergone and are still under- 
going from the moment that they begin to be covered 
more or less thickly with other more recent deposits. 

Now a very thick covering with recent deposits can 
only be the consequence of a previous depression. But 
by the combined effect of depression and the weight of 
fresh deposits the underlying strata are subjected not only 
to an increased pressure but also an increased temperature. 

In the earliest periods of the earth's development, 
there probably was also an increased pressure from a 
denser and more heavily laden atmosphere, and besides 
the increase of heat with the depth from the surface, 
there was doubtless a generally higher temperature of the 
whole globe, so that the difference which now exists 
between older and more recent igneous rocks, and be- 
tween volcanic and plutonic rocks, would at that time 
be much smaller, all volcanic formations partaking more 
or less of the nature of the plutonic. 



384 PROCESSES OF ROCK FORMATION: 

Therefore, pressure and heat, with the addition, per- 
haps, of water (which has either penetrated the earth to 
a considerable depth or which chemically formed a part of 
its original composition), appear to have worked together 
through great periods of time to produce the final result 
of the transmutation into crystalline schist; and those 
crystalline schists which are now to be seen on the earth's 
surface must also have been lifted and partially deprived 
of their superincumbent masses. But as each process of 
covering, of transmutation, of raising and re-exposure, 
must have occupied extensive periods of time, it follows 
that all crystalline slates which are now accessible to ob- 
servation are of very ancient formation. In general lan- 
guage, they may be said to represent the oldest deposits 
in a metamorphosed state. Exceptions to this character 
can only be attributed to special circumstances. In the 
Alps, such exceptions do appear to have taken place. The 
deposits of the Jurassic, the Chalk, and the Tertiary periods 
exhibit there an extraordinary thickness of development, 
and, consequently, belemnitic strata (of the oldest deposits 
of the Jurassic period) appear in certain places to have been 
so thickly covered as to have been changed into crys- 
talline schist ; and very energetic upliftings have also at 
a later period exposed them. 

In general we may say of the Alps, that the process of 
metamorphosis has been there pushed up higher in the 
scale of the earth's history than elsewhere is usual. The 
Eocene deposits contain firm clay-slate, which is used for 
roofing purposes ; the Miocene browncoals of the Mo- 
lasse formation appear already to have almost become 
ordinary black coal, &c. On the other hand, we find the 
converse of this state of things in the low lands of Russia, 
where the oldest Silurian formations are still partially in 
the state of plastic clay and friable sandstone, probably 
because they have never been thickly covered. 

The temperature to which the lowest deposits have been 
subjected, under very great pressure of thicklying super- 
incumbent masses, may even have reached so great a 
degree that some or all of the rocks composing such strata 
have been softened or perhaps partially fused. In this way, 
for instance, we may explain the otherwise singular pheno- 
menon of layers of granular limestone which sometimes 



METAMORPHIC SCHISTS. 385 

lie between beds of crystalline schist; yea, even sili- 
ceous rocks may have been softened by this means, en- 
tirely losing their slaty texture and stratification. 

No doubt, we may be easily led by such speculations 
into regions of unfounded hypothesis, but the causes to 
which we have referred afford a possible explanation of 
many bedding relations between granulite and gneiss, 
which cannot be accounted for by simple transmutation 
from a sedimentary formation. 

Now, granted that we are able to explain the special 
state of the crystalline schists by such general plutonic 
influences as pressure and heat, there yet remains the im- 
portant question whether their chemical composition also 
corresponds with this theory of their transmutation; in 
other words, whether the sedimentary rocks originally 
contained, or could have subsequently absorbed, those in- 
gredients which were necessary to the formation of the 
crystalline schists. In many of the sedimentary rocks this 
is most certainly the case. We need only compare the 
ingredients of the crystalline schists with those of the as 
yet uncrystalline slates as given in the tables, p. 86, 
ante, in order to perceive that, even without the accession 
of new ingredients or parting with any which they now 
contain, many a clay-slate might be changed into a mica* 
schist, and others into a gneiss, if their ingredients could 
be so disposed as to combine into crystalline mineral ag- 
gregates. The elements are there; the opportunity of 
assuming a new shape is the only thing wanting. The 
composition of different clay-slates, several of which also 
contain some lime and magnesia, corresponds with that 
of many different varieties of gneiss, mica-schist, and 
hornblende-schist. Doubtless an additional quantity of 
magnesia would be necessary to the formation of the 
chlorite and talcose schists, but the possibility of the ac- 
cession of solutions of magnesia is proved beyond doubt 
Ity llie existence of numerous pseudomorphs of certain 
well-known minerals. With reference to the formation of 
these magnesian rocks (to which serpentine also belongs), 
certain special conditions would appear to have been ne- 
cessary in their case in addition to the general causes 
which contributed to the formation of the great mass of 
the other crystalline schists. 

c c 



386 PKOCESSES OF KOCK FORMATION : 

Our hypothesis (to which, however, we lay no personal 
claim) by no means excludes the possibility of water as an 
auxiliary agent in such transmutations as we have de- 
scribed. The comparatively recent experiments of Daubree 
have established that water will remain in combination 
with other substances, such as silicates, under high atmo- 
spheric pressure, even at a white heat ; and that in such 
cases it even materially affects the fusing point of sub- 
stances ; and Scheerer has proved that the water con- 
tained in the mica of gneiss was a part of its original com- 
position. This water may have caused many phenomena 
in the interior of the earth, which as yet we are not able 
accurately to explain or prove. 

What thickness of superlying strata should be assumed 
as sufficient to produce the transmutation which has re- 
sulted, we are unable to say ; and we have fewer data for 
any computation, as, according to the igneous theory of 
the earth's formation, the average temperature of the 
whole globe, including the surface, must formerly have 
been much higher, and the atmosphere more compact and 
dense, therefore the pressure much greater, than at the 
present day. Moreover, in all geological phenomena 
the duration of a particular influence will to some ex- 
tent supply any deficiency in its energy ; and, as we have 
no standard by which to measure the time of geological 
processes, we have free scope to assume any duration of 
time that appears necessary to explain their operation. 

The crystalline schists, if we take their principal repre- 
sentatives, gneiss and mica-schist, are more closely allied 
to the acidic than the basic igneous rocks. The cause of 
this is easily explained. In the igneous rocks, the two 
principal bases, whose greater or less proportion chiefly 
creates the distinction between the acidic and basic groups, 
are lime and magnesia. Now, on the decomposition or 
disintegration of the igneous rocks, their lime and mag- 
nesia having first been taken up in solution (for the most 
part in combination with carbonic acid), have then been 
separately deposited in the form of independent beds of 
limestone and dolomite. The aluminous and quartzose 
ingredients of the igneous rocks have formed the more 
mechanical deposits of clay and sand, free from lime, and 
appear to have produced the greater part of the crystal- 






METAMORPHIC SCHISTS. 387 

line schists ; and as the calcareous and magnesian deposits 
were originally formed between the strata of clay and 
sand, so we again meet with limestone and dolomite rocks 
imbedded between the acidic crystalline schists ; and we 
may assume that they represent the collective amount of 
lime and magnesia in which the average of the crystal- 
line schists is deficient as compared with the average of 
the igneous rocks. This separate development of the 
lime and magnesia may likewise be the reason why com- 
binations of hornblende, pyroxene, and labradorite are, 
generally speaking, far less frequent in the crystalline 
schists than in the igneous rocks. 

The crystalline schists, according to our theory, must 
represent the most ancient or undermost deposits of the 
world's history. They are the oldest rocks of which we 
have knowledge, since we find them overlaid by all the 
sedimentary rocks, and broken through by every kind of 
igneous rock. But the question arises, upon what foun- 
dation can these deposits have first rested, if no other 
rocks were previously in existence? Doubtless there 
must have previously existed a firm foundation or floor of 
deposit separating the fused mass of the interior from the 
covering of water and air, by whose means alone deposits 
could be formed. If, therefore, we acknowledge the fused 
state of the whole earth as its most ancient geological 
condition, we are necessarily led to assume the existence 
of a very thick first crust, caused by the cooling of the 
surface of this molten matter before it would be possible 
for any sedimentary or eruptive rocks to form. Now 
what has become of this first crust, unless it be repre- 
sented by the crystalline schists ? It is certainly difficult 
categorically to answer a question of this nature, refer- 
ring to ages and circumstances long since passed; but 
one thing is certain, viz. that such gneiss, mica-schist, or 
argillaceous mica-schist, as contain parallel subordinate in- 
terlying beds of limestone, dolomite, hornblende-schist, 
quartz-schist, ironstone, or graphite, and the like, can- 
not have been formed by the first cooling of the earth's 
mass. No doubt where such interlying beds are entirely 
absent, as, for instance, in some gneiss, it is possible that 
such districts may be the remains of a first crust of the 
earth. Further, it is not certain that all granite is of 

c c 2 



388 PROCESSES OF EOCK FORMATION: 

eruptive origin ; indeed, there are many circumstances 
that point to a contrary assumption in certain districts. 
Here, therefore, we have something which may possibly 
date from the first cooling of the earth's surface. But 
uniform districts of gneiss containing no foreign subordi- 
nate beds, and granite districts without recognisable 
traces of eruptive origin, are phenomena so rare to our 
present geological experience, that they evidently do not 
suffice to represent a great primeval crust of the earth. 
Under these circumstances, there seems nothing left for 
us in the present state of our knowledge but to assume 
that the greater part of the first crust, having become 
very thickly covered with deposits, has been gradually 
remelted and become eruptive, perhaps in the form of 
granite. There is, indeed, no reason why the same fate 
should not have been shared by the oldest rocks of de- 
posit ; and thus it may be that the chronological starting- 
point of geological development has frequently been 
effaced, and become altogether uncertain. 

In what we have said above, we have endeavoured to 
develope the plutonic theory of the origin of crystalline 
schists. Recently, however, other explanations of the 
origin of those rocks have been started, not so much by 
geologists as by chemists, who also assume their origin 
by transmutation from sedimentary rocks, and differ from 
the geologist chiefly in denying all plutonic agency, only 
acknowledging the efficacy of such chemical processes as 
might have taken place under the conditions existing at 
the surface of the globe. 

We have already more than once shown, in the course 
of this work, that plutonic processes do not exclude the 
combined action of water as an auxiliary agent ; and thus 
may deserve the name of HTDROPLUTONIC; but, according 
to the more recent views of some chemists, water alone is 
said to suffice, under circumstances of ordinary pressure 
and temperature, to have brought about these transmu- 
tations in the course of time. 

We do not venture to pronounce upon such theories 
from a chemical, but only from a geological point of view, 
and in this respect they do not satisfy our mind, chiefly 
because they disregard the effect and influence of very 
thick overlying strata, therefore of high pressure and 



METAMORPIIIC SCHISTS. 389 

increased temperature ; because they do not explain why, 
for instance, in the Alps, very recent deposits are greatly 
altered in character, whereas in other countries very old 
deposits where they have remained uncovered are scarcely 
changed at all (as, for instance, in Northern Russia); 
and finally, because they leave the phenomena of con- 
temporaneous mechanical changes, such as condensation, 
slaty structure, &c., entirely unexplained. Assuming it 
to be the fact that by the agency of water alone, under 
circumstances of ordinary pressure and temperature, mica- 
schist or gneiss, hornblende-schist, &c., might be produced 
from clay (argillaceous shale or clay-slate), it would still 
be difficult to believe that by such agency proceeding from 
the surface, whole complicated systems of strata should 
not have been more locally influenced, and very differently 
affected at different depths, instead of having been almost 
everywhere equally and uniformly influenced by the trans- 
forming cause. Again, if all these important changes 
and transmutations were entirely or chiefly due to water, 
it would be very extraordinary if we did not find that 
they had been occasionally modified by the increase of 
temperature and of pressure to which they must have been 
subjected, since we cannot shut our eyes to the existence of 
such influences in the interior of the earth, and numerous 
geological facts sufficiently prove that many rocks which 
once were very thickly covered have been subsequently 
laid bare by processes of uplifting and denudation. 

If we adopt the pure chemical hypothesis, then we must 
abandon the idea of that relationship existing between 
bedding and transmutation which, according to the plutonic 
theory, is an invariable law. It is indeed somewhat sus- 
picious that the supporters of the chemical theory, in 
order to make the plutonic appear improbable, almost 
entirely dispute as a fact the operation of pressure and in- 
creased temperature in the interior of the earth, whereas 
every unprejudiced person acquainted with the rudiments 
of physics must admit these forces to exist inevitably 
under the given circumstances. The same persons are 
even in the habit of disputing the eruptive character of 
the greater number of igneous rocks, from which we 
infer that they are deficiently acquainted with geological 
facts from personal observation. We purposely use the 



390 PROCESSES OF ROCK FORMATION: 

word eruptive (not igneous) because the eruptive cha- 
racter of the rock is unmistakably proved by the form of 
its mass, even if occasional doubts should arise as to the 
actual state of some few rocks at the time of their in- 
trusion. 

In other words, we do not regard those chemists very 
competent guides in pure geological questions, who fail 
adequately to regard the external phenomena of form and 
bedding no less than the elementary composition of rocks. 

We would not be understood to depreciate the careful 
experiments and researches which we owe to Gr. Bischof 
and others on the effect of water in the processes of for- 
mation and transmutation of minerals. These are highly 
instructive, and they are more especially valuable as 
clearing up and explaining very scientifically what was 
previously only matter of surmise respecting the nature of 
the process of formation of mineral deposits in vesicular 
cavities and fissures of some rocks, and respecting the 
special formation and transmutation of minerals in the 
interior of other rocks, by which latter process, for in- 
stance, serpentine, chlorite-schist, talcose schist, &c., may 
in many instances have resulted. 

In the course of these observations mention has been 
made of transmutation by means of contact ; i. e. of such 
transmutations as are found at the margin or in the 
neighbourhood of eruptive igneous rocks which have 
broken through sedimentary rocks. That such exist 
cannot be doubted ; as a rule, however, they extend to 
only a very limited distance from the eruptive rock. 
They may be divided into such as are purely plutonic or 
hydroplutonic, and such as are volcanic processes. To 
the plutonic processes belong the formations of hornstone, 
nodular schist (Knotenschiefer), and chiastolite-slate on 
the contact-margins of granite or greenstone. To the 
volcanic processes belong special induration, slacking, 
vitrefaction, coking and columnar jointing of argilla- 
ceous sandy or carboniferous rocks on the margins of 
basalt, trachyte, or porphyry. These latter cases appear 
to be simply the result of greatly increased temperature 
and subsequent rapid cooling without water. The plu- 
tonic processes, on the other hand, admit of the combined 
agency of water and heat. 



METAMORPHIC SCHISTS. 391 

Transmutations occasioned by the burning of beds of 
coal (as the burnt clays, described p. 338, ante) are pro- 
cesses of entirely local character, and there may be many 
other such which it is unnecessary further to describe for 
our present purpose. 

The transmutations of which we have hitherto spoken are 
chiefly such as have taken place in the interior of the earth 
with exclusion of atmospheric air. For these Haidinger 
has proposed the term catogenic in contradistinction to 
the anogenic transmutations which proceed from the ex- 
terior towards the interior, under the influences of air and 
water. These latter correspond in part with the very 
general process of weathering the rocks ; they do not, 
however, always consist in the decomposition or disin- 
tegration of the masses affected, but sometimes rather in 
the formation of hydrates. To this belong the coalescing 
of the felspathic rocks, the formation of wackes by means 
of compounds containing augite or hornblende, the for- 
mation of gypsum from anhydrite, &c. These anogenic 
transmutations likewise play an important part in the 
chain, of processes by which in nature matter circulates 
through its various forms. 

The most striking of the contrasts between the cato 
genie and anogenic transmutations may be stated some- 
what in the following manner : 

Catogenic. Anogenic. 

Condensation and induration. Disintegration. 

Crystallisation. Frequent destruction of the crys- 

talline state. 

Deoxidation. Oxidation. 

Loss of water (to a certain Formation of hydrates. 

extent). 

Formation of slaty schistose or 
texture. 

The following recent works may be here cited as espe- 
cially noteworthy upon the metamorphosis of rocks : 

St. Claire Deville, the Operation of Chlorides and Sulphates upon 
the Metamorphism of the Sedimentary Rocks, Compt. rend. 
1858, vol. xlvii. p. 89. 

A. Gages, on the Study of some Metamorphic Rocks, Philos. 
Mag. 1859, March, p. 169. 

O. Lieber, Critique on the Views of Bischof and Naumann on 
the Subject of Metamorphism. in Mining Mag. vol. i. Decem- 
ber 1859. 



392 PROCESSES OF ROCK FORMATION. 

Delesse, Etudes sur le Metamorphisme des Roches, Paris, 1861 : 
v. L. u. Br. Jahrb. 1858, pp. 335 and 727, 1859, pp. 222 and 
223 ; 1'Institut, 1861, p. 276. 

Daubree, Etudes sur le Metamorphisme et sur la Formation des 
Koches Cristallines, Paris, 1860. 



MINERAL VEINS AND VEINS OF ORE. 

These almost form a special group of rocks, and would 
be entitled to an equal place by the side of the three 
other groups, if the extent of space which they occupy in 
nature were not so small. They but fill up narrow fis- 
sures in other rocks. Their origin appears, almost with- 
out exception, to have been hydroplutonic. They are, for 
the most part, chemical precipitates from aqueous solu- 
tions formed in the interior of the earth under very dif- 
ferent circumstances of pressure and heat than those 
which prevail upon the surface. 

Having treated these formations, which occupy so sub- 
ordinate a space in the composition of the earth's crust, 
at length in our book on ' Erzlagerstatten,' we shall not 
devote further space to them here. 



CONCLUSION. 

BEARING in mind the facts and considerations above 
stated, if we take a general review of the various forma- 
tions and transformations of rocks, we shall discover in 
them a perpetual process of circulation or rotation of 
substances, and of their different states. The substances 
remain, but the forms in which they appear and the mode 
of their combinations vary. 

Disregarding for the moment the first solid products 
of cooling on the earth's surface, as not being capable of 
identification at the present day, we may most conve- 
niently enter the circle of transmutations with the erup- 
tive igneous rocks, as approaching most nearly to original 
formations. These then are constantly attacked and de- 
composed by chemical and mechanical forces acting from 
their surface inwards, and from their cracks and fissures 
outwards. 

The products of this decay are deposited either in the 
form of chemical precipitates or mechanical aggregates. 
By chemical process of precipitation cavities and fissures 
in rocks become filled up (amygdaloids and veins), depo- 
sits are made at the mouths of springs of limestone-tuff, 
siliceous tuff, bog-ore, &c. ; or else, other crystalline rocks 
are formed, such as gypsum or rock-salt. By mechanical 
agency, on the other hand (partly aided by organic pro- 
cesses), there arise the much more important and exten- 
sive deposits of clay, sand, pebbles, marl, limestone, and 
dolomite ; and during the process of deposit, carbon (in 
the form of carbonic acid from the atmosphere), water, 
chlorine, and some other substances are added to the pre- 
viously existing materials. 

But, like the eruptive masses, all these deposited masses 
in their turn are partly decomposed and washed away by 
external forces, and in other part they become greatly 
changed internally by pressure and the action of heat. 



394 PROCESSES OP EOCK FORMATION. 

By means of heat and pressure acting during long periods, 
parts which thus in the first instance were only mecha- 
nically bound together, enter into new chemical com- 
binations with each other, and assume a crystalline state 
more or less analogous to that of the crystalline mineral 
aggregates of the eruptive rocks. It is even pro- 
bable in many cases that the substance of these deriva- 
tive rocks has been fused and become eruptive a second 
time. 

Thus the process of destruction and new formation of 
rocks, be it ever so slow, and therefore difficult of ob- 
servation, has never, at any time of the earth's history, 
been interrupted, but continues at the present day ; and 
not only is this true of the original formations, but the 
new products of consolidation, of deposit, and of transmu- 
tation have always been equally subjected, and are still 
subject, to the same processes. 

This is the perpetual circulation of matter in the world 
of rocks. 

In the course of such various and renewed working up 
and transformation of the same substances, with the addi- 
tion of those others furnished by the air and water, it 
cannot be matter of wonder that the variety of their 
groups has been always somewhat on the increase ; for, if 
certain processes in this rotation are altogether universal 
in their character, recurring in the same way, everywhere 
and in every age, yet in consequence of the general mul- 
tiplication of conditions and circumstances, and the in- 
creasing aggregate of their results, special combinations 
of the same processes have constantly arisen in later times 
and brought about special formations of rocks which were 
not previously in existence, or which do not belong to 
the normal phenomena of nature. 

This increase in variety of the products of later times 
is not confined to geological and mineral substances ; a 
greater and more rapid increase has taken place in the 
organic world, where the forms of life have multiplied in 
an ever ascending ratio (partly in consequence of the 
change and increase of the conditions of existence from 
geological causes). 

The processes of change, to which the outward con- 
formation of the globe's surface is subject, likewise mul- 



CONCLUSION. D95 

tiply more rapidly than mere strictly geological pheno- 
mena. 

Reasoning, therefore, from the past and from analogy 
with other kingdoms, we must expect the species of rocks 
and kinds of rock-formation to go on increasing inde- 
finitely for the future, as they have been increasing con- 
tinually ever since the first solidification of our earth's 
crust. 



INDEX OF LOCALITIES. 



AAC 

* ACFIEN, smithsonite of, 34 
** Aberdeenshire. andalusite of, 35 
Adamello Mountains, in Southern Tyrol, 

tonalite of, 207 
Adam's Peak, Ceylon, oligoclase-gneiss 

of, 239 

jEcrjna, trachyte of, 186 
.<Etna, alum, near the crater of, 50 

dolerite of, 137 

hematite of, 63 

labradorite in the lavas of, 1 1 

trachyte of, 186, 188, 192 
Africa, limestone of, 282 

lower chalk of, 283 

nummulitic limestone of, 282, 283 

trona of, 59, 352 

Acordo, in the Alps, pyrites of, 358 
Aix-la-Chapelle, galmey of, 356 
Ajaccio, diorite of, 155 
Albanian Mountains, leucite rock of, 
143, 186 

peperino of the, 308 

Algarve, in Portugal, foyaite of, 181 
Algeria, nummulitic limestone of, 282 
Alleghany Mountains, anthracite of, 336 
Allgau, allogorite of, 142 
Almaden, in Spain, cinnabar of, 358 
Alps, adularia of the, 9, 201 

alpiniteof the, 239 

analcime of the Seisser Alp, 30 

anhydrite of the, 48 

browncoal of the, 330 

chlorite-schist of the, 250 

dolomite of the, 289 

firn or ne\e of the, 346 

fluor-spar of the, 69 

gneiss of the, 239 

granite of the, 206, 207 

greenovite of the, 47 

gypsum of the, 49, 292, 293 

limestone of the, 283, 284 

chalk formation of the, 283 

melaphyre of the. 163 

mica-schist of the, 244 

nagelflue of the, 303 



AME 
Alps continued 

red sandstone of the, 300 

pebbles at the foot of the, 102 

potstone of the, 251 

pyrites of the, 358 

roofing slates of the, 265 

shale of the, 267, 268 

sandstone of the, 299 

talc-schist in the, 252 

mica-schist of the Eastern, 244 

celestine of the Seisser, 48 

Alps, Northern, breccia-like rocks of, 305 

dolomite of the, 289 

glauconite of the, 27 

marl of, 274 

Alps, Pennine, dolerine of the, 252 
Alps, Western, spilites of the, 167 
Alpujarras, in Spain, galena of, 70 
Alston Moor, aragonite of, 58 
Altai Mountains, porphyrite of the, 170 
Altenberg, in Saxony, chlorite of, 25 

granite-porphyry of, 214 

granular limestone near, 277 

greisen near, 321 

Zwitter rock of, 322 

pycnite of, 354 

Altenhain, in the Erzgebirge, granite- 
porphyry of, 213 
Amberg, yellow earth of, 356 
America, limestone of, 283 

lower chalk of, 283 
America, North, alunogen of, 50 

apatite of, 53 

blue spinel of, 61 

catawbirite of, 345 

chromic iron-ore of, 62 

franklinite of, 357 

hornblende-schist of, 254 

mispickel, of, 74 

nncritide of, 244 

itacolumite of, 249 

naphtha of, 77 

orbitoidal limestone of, 283 

petroleum or rock-oil of, 337 

rutile of, 66 



INDEX OF LOCALITIES. 



AME 

America, North tontinued 

specular iron of, 343 

titanite of, 47 

trona of, 59 

America, South, andesite of, 192 

felspar rocks of, 188 

itacolumite of, 248 

trachyte of, 186 

Amiano, in Parma, naphtha of, 77 
.Andernach, on the Eliine, leucite rock 
near. 143 

titauite of, 47 
Andes, andesine of the, 1 1 

felspar rocks of the, 188 
Andreasberg, analcime of, 30 

anhydrite of, 48 

apophyllite of, 30 

harmotome of, 32 

Antisana, in South America, andesite 
of, 192 

trachyte of, 186 

Antrim county, granular limestone of, 278 

phillipsite'of, 32 
Arabia, turquois of, 54 
Aragon, nitre of, 55 

Ararat, Mount, andesite of. 192 
Ardennes, ottrelite-schist of the, 256 
Arendai, in Norway, apatite of, 83 

graphite of, 75 

magnetic iron- ore of, 61, 345 

pistacite of, 42 

scapolite of, 42 

titanite of, 47 
Argyleshire, titanite of, 47 
Arksatfiord, in West Greenland, cryolite 

of, 69 

Artern, in Thuringia, mellite of, 77 
Ascbaffeaburg, gneiss of, 239 

granite-porphyry of, 213 

titaniferous iron of, 63 
Asia Minor, corundum of, 351 

nummulitic limestone of, 283 
Aue, in Saxony, kaolin of, 354 
Auerbach near Heidelberg, granular 

limestone of, 278 
Auerbach, in the Odenwald, kinzigite 

of, 320 

Aulgasse, in Siegburg, dolerite of, 135 
Aussig, in Bohemia, natrolite of, 32 

phonolite of, 200 

Autun, in France, bituminous sub- 
stances of, 77 
Auvergne, alunite of, 52 

apophyllite of, 30 

colourless hyalite of, 8 

scolecite of, 33 



BER 

Auvergne continued 

zircon of, 41 

Averno, Lake of, leucite of, 185 

Azores, trachyte in the lavas of the, 190 



BADEN, pyrochlore of, 45 
perofskite of, 45 

Ballybrack, near Dublin, granite of, 206 
Baltic, amber on the coasi of the, 76 
Bannat, apophyllite of the, 30 

coal of the, 334 

Barenburg, in the Erzgebirge, granite- 
porphyry of, 213 

Barnstaple, in Devonshire, wavelliteof, 55 

Barre, in Massachusetts, rutile of, 66 

Barton clay, 270 

Baste, in the Hartz Mountains, schil- 
ler-spar of, 19 

schiller-rock of the, 316 
Bath, stone of, 280 
Bavaria, apatite of, 53 

cordierite of, 44 

columbite of, 46 

flint in the Upper White Jurassic 
of, 6 

glauberite of, 49 

graphite of, 336 

kinzigite of, 320 

nodular limestone of, 280 

opal of, 349 

ottrelite-schist of, 256 

siliceous spherosiderite of the Alps 
of, 346 

slaty limestone of, 281 

vivianite of, 54 

Baveno, common felspar of. 10 
Baveno, in the Alps, granite of, 206 
Belfaly, in the Vosges, aphanite of, 160 
Bell, near Andernach, leucite rock of, 143 
Bellmansloos, near Tharand, felstone of, 

222 
Belmsdorf, in Oberlausitz, aphanite of, 

161 

diorite of, 155 

Berchtesgaden, in Bavaria, glaubersalt 
of, 51 

glauberite of, 49 

Beregheacz, in Hungary, alum-stone of, 
309 

trachyte-porphyry of, 195 
Beresowsk, in the Ural, beresite of, 207 

talc-schist of, 252 
Berggieshiibel, in Saxony, magnetic 

ironstone of, 345 
Berlin, glauconite of, 27 



INDEX OF LOCALITIES. 



399 



BER 

Berneck, in the Fichtelgebirge, diabase 
of, 147 

mica-schist near, 244 

gneiss near, 239 

Bex, in Switzerland, gypsum of, 293 
Bilin, in Bohemia, aragonite of, 58 

opal found in the tripoli of, 8 

rock-soap of, 355 

semi-opal of, 349 

Binnen Thai, in the Alps, dolomite of 

the, 289 

Birkenlioff, red melaphyre of, 166 
Black Forest, kinzigite of the, 320 
Blanc, Mont, gneiss of, 239 
Blattendorf, in Bohemia, phonolite of, 

200 
Bleiberg, in Carinthia, galena of, 70 

smithsonite of, 34 
Blumau, porphyry of, 218 

Bocche, Monte, in Tyrol, porphyry of, 

218 
Bodenmais, beryl of, 39 

columbite of, 46 

cordierite of, 44 

kinzigite of, 320 

vivianite of, 54 
Bognor, clay of, 270 
Bohemia, alum of, 50 

amber of, 76 

apatite of, 53 

aragonite of, 58 

basalt of, 141, 142 

bituminous substances of, 77 

colourless hyalite of, 8 

egeran of, 318 

epsomite of, 50 

felspar of, 10 

glaubersalt of, 51 

gneiss of, 238, 239 

granite of, 202 

granulite of, 231 

granulite-gnei*s of, 238, 239 

marcasite of. 73, 357 

marl of, 273 

mellite of, 77 

mica-schist of, 242 

natrolite of, 32 

phonolite of, 187 

phonolites of, 198, 200 

polianite of, 65 

polishing slate of, 350 

pyrope of, 41 

rock-soap of, 355 

sandstone of, 299 

thomsonite of, 31 

titanite of, 47 



CAN 

Bohemia continued 

wavellite of, 55 
Bb'hmisch-Wiesemhal, leucite rock of, 

143 
Bohrineen, in Saxony, gabbro of, 151 

serpentine of, 317 
Bologna, barytes near, 48 
Bonhomme, Col du, albite of, 11 
Bonn, alunogen of, 50 

bituminous substances of, 77 

trachyte of, 184, 190 
Borghetto, leucite of, 186 
Borrowdale, in Cumberland, graphite of, 

75, 336 

Borsabanya, in Hungary, timazite of, 156 
Boston, in Massachusetts, potstone ot, 

251 

Botallock, in Cornwall, axinite of, 44 
Botzen, in the Tyrol, laumontite of, 32 

porphyry of, 218 

Boxdorf, near Moritzburg, granite-gneiss 
of, 238 

Brambach, in the Voigtland, granite- 
gneiss of, 238 

Brandau, in the Erzgebirge, anthracite 
of, 336 

Brandholz, in the Fichtelgebirge, mica- 
schist near, 244 

Brava, Island of, nosean of, 15 

Brazil, Carveira of, 234 

itabirite of, 343 

itacolumite of, 248 

moorshead rock of, 343 
Brest, kersanton of, 175 

Brevig, in Norway, pyrochlore of, 45 

wohlerite of, 46 

zircon-syenite of, 181 
Briesgau, jasper of, 6 

granular limestone of, 278 
Britain, felstone of, 222 
Brittany, kersanton of, 175 

staurotide of, 36 

Brixen, in the Tyrol, granitite of, 207 
Bronzell, in Tyrol, porphyry of, 218 
Bnchenberg, in the Uartz, wernerite 
rock of, 222 



, stone of, 280 
Calabria, nitre of, 55 
Calais, glauconite of, 27 
California, borax of, 53 

naphtha of, 77 

Canada, chloritoid schist in, 251 

naphtha of, 77 

serpentine rocks of, 317 



400 



INDEX OF LOCALITIES. 



CAN 

Cantal, in France, schistous trachyte of, 

184 
Capo Loneo, south of. St. Gotthard, 

tourmaline of, 37 
Caradoc, sandstone of, 301 
Carinthia, galena of, 70 

smithsonite of, 34 

Carlsbad, in Bohemia, aragonite of, 58 

common felspar of, 10 

fibrous limestone of, 281 

glaubersalt of, 51 

granite of, 205 

marcasite of, 73 

orthoclase of, 354 

peastone of, 280 
Carolina, itacolumite of, 249 

catawbirite of, 345 

Carpathian Mountains, chlorite-schist of 
the, 250 

limestone of the, 284 

sandstone of the, 299 

shale of the, 267 

Carrara, common quartz in the marble 

of, 6 

Castelruth, porphyry of, 218 
Castleton, in Derbyshire, elaterite of, 77 
Catini, Monte, in Tuscany, trachyte of, 

184 
Caucasus, andesite of the, 192 

trachyte of the, 186 

Cavalessi, in Southern Tyrol, porphyritic 

rocks of, 170 

Cevennes, fraidonite of the, 175 
Ceylon, nitre of, 55 

oligoclase-gneiss of, 239 

precious corundum of, 8 

spinel of, 61 

Chaux, near Frejus,blue porphyry of, 171 
Cheltenham, pea-grit of, 280 
Chemnitz, in Saxony, chlorite-schist 
near, 250 

porphyry near, 217 
porphyry-tuff of, 309 

Chessy, near Lyons, malachite of, 60 
Chiavenna, potstone of, 251 
Chili, nitratine of, 55 
Chimborazo, andesite of. 192 

trachyte of, 186 
China, agalmatolite of, 354 

precious corundum of, 8 

Cilli, in Styria, fullers' earth of, 356 
Cimini Mountains, trachyte of the, 184 
Clermont. trachyte near, 186 
Colima, Mount, in Mexico, trachyte of, 

186 
Commern, in the Eifel, galena of, 70 



DIP 

Compain, Pas de. in France, schistous 

trachyte of, 184 
Connecticut, chabasite of, 31 

columbite of, 46 

Corbitz, near Meissen, pitchstone of, 224 
Cornwall, axinite of, 44 

common felspar of, 1 

common quartz of, 5 

greisen of, 321 

kaolin of, 13 

malachite of, 60 

marcasite of, 73 

quartz-porphyry of, 219 

saponite of, 26 

titaniferous iron of, 64 

topaz of, 36 

tourmaline of, 38 

vivianite of, 54 
Corsica, anorthite, of, 12 
=- diorite of, 155 

porphyry of, 218 
Cotopaxi, andesite of, 192 

trachyte of, 186 
Criffel, zircon of, 41 
Crimea, meerschaum of, 354 
Croatia, sulphur of, 358 

Csetatye, in Transylvania, porphyry of 

219 
Cumbal Euca Pichincha, in South 

America, trachyte of, 186 
Cumberland, chiastolite-schist of, 257 

galena of, 70 

graphite of. 75, 336 

limestone of, 285 

Cyclopean Islands, near Sicily, analcime 
of the, 30 



TvANEMORA, in Sweden, magnetic 

J ironstone of, 61, 345 
Danube, gneiss on the, 239 

granite on the, 207 
Dead Sea, asphalte of the, 77 

bitumen of the, 337 
Derbyshire, dolomite of, 290 

elaterite of, 77 

galena of, 70 

smithsonite of, 34 

Desert, jasper in the sand of the, 6 
Devonshire, andalusite of, 35 

wavellite of, 55 

Dilln, near Schemnitz, agalmatolite of, 

354 
Dippoldiswalde, in Saxony, felstone of, 

222 

gneiss of, 239 



INDEX OF LOCALITIES. 



401 






DIP 

Dippoldiswalde continued 

minette of, 174 

Ditro, in Transylvania, syenite of, 179 

wohlerite of* 46 

Domokos. in Transylvania, pyritesof, 358 
Dore", Mont, augite of, 185 
Bore's, Monts, in Ve'lay, trachyte of, 184 
Dossenheim, in the Odenwald, granite 

of, 207 
Draclienfels, sanidine of the, 10 

trachyte of the, 184, 185, 190 
Dresden, alunogen of, 50 

gneiss near, 238 

hornblende- porphyrite of, 171, 172 

laumontite, 32 

oligoclase of, 11 

orthite of, 43 

syenite near, 176, 178, 179 
Drontheim, in Norway, potstone of, 251 
Drusenthal, in the Timringian Forest, 

granite-porphyry of, 207 
Dublin, freestone of, 298 

granite near, 206 
Dumbartonshire, analcime of, 30 

prehnite of, 31 

thomsonite of, 31 

laumontite of, 32 
Dunse sandstones, 300 
Dura-den sandstones, 300 

Durance, variolitic aphanites of the, 159 
Durham, dolomite of, 290 



EBERSDORF, in Saxony, coal of, 
333 

Ebnat, in Bavaria, ottrelite-schist of. 256 
Kdenville, in New York, rutile of, 66 
Edinburgh, porphyry near, 170 
Eibenstock, in the Erzgebirge, granite 
of, 206 

mica-schist of, 244 

schorlaceous schist of, 323 
Eifel, galena of the, 70 

trachyte of the, 191 

Eger, in Bohemia, egeran of, 318 

granite of, 205 

k'ranulite-gneiss of, 238, 239 

gneiss -f, 239 

mica- schist of, 243 
Egypt, chrysolite of, 38 

natron of, 59 

nummulitic limestone of, 283 
Elba, Island of, epidosite of, 355 

lievrite <f, 37, 356 

specular iron of. 343 
Elbingerode, in the Hart a, graphite of, 75 

labradorite-porphyry of, 160 



FAR 

Elfdalen, in Sweden, chrysolite of, 39 
hypersthenite of. 152 

porphyrite of, 170 

Elgersburg, in Thuringia, braunite of, 

64 

Ellenbogen, granite of, 205 
Engadine, serpentine of the, 317 
England, dolomite of, 289, 290 

flint in the chalk of, 6 

gypsum of, 293 

limestone of, 278 

marl of, 273 

Portland stone and oolite of, 284 

sandstones of, 298, 299 

upper and lower chalk of, 283 

Wenloc-k shale of, 268 

clays of, 270 
Epsom, epsomite of, 51 
Erlbachgrund, in Saxony, dichroite rock 

of the, 320 

Erbendorf, porphyry near, 218 
Erzgebirge, actinolite-srhist of the, 254 

corundum of the, 351 

gneiss of the, 233. 234, 236, 239 

granite of the, 206 

granite-porphyry of the, 213 

greisen of the, 321 

mica-schist of the. 243. 244 

mica-trap rocks of the, 173 

nodular or spotted schist of the, 257 

phonolite-tufa of the, 309 

porphyry of the, 217, 218 

protogine of the, 206 

quartz-breccia of the, 305 

serpentine of the, 317 

talc-schist of, 252 

Essex, amber on the coast of, 76 
Euganean Hills, Lombardy, trachyte of, 
184 

trachyte-porphyry of the, 195 
Europe, lower chalk of, 283 

nummulitic limestone of the South 
of, 282 

Evigtok, in Greenland, cryolite of, 353 



FAHLUN, in Sweden, automolite of, 61 
gadolinite of, 43 

mica-schist of, 242 

pyrites of, 358 

Fahrnleiten, in the Fichtelgebirge, gra- 

nulite- gneiss of, 239 
Faroe, apopliyllite of, 30 

chabasite of, 31 

heulandite of, 33 

laumontite of, 32 

stilbite of, 33 

D 



402 



INDEX OF LOCALITIES. 



FAS 

Fassa Thai, apophyllite of, 30 

augite-porphyry of, 160 

chabasite of, 31 

heulandite of, 33 

idocrase of, 41 

melaphyre of, 163 

prehnite of, 31 

stilbite of, 33 

Fetlar, Island of, chromic iron -ore of, 62 
Fezzan, in North Africa, trona of, 352 
Fichtelgebirge, aphanite of the. 159 

chiastolite-schist of the, 257 

chlorite-schist of the. 250 

diabase of the, 147-149 

eklogites of the, 318 

gneiss of the, 239 

granite of the, 202, 205, 207 

granulite-gneiss of the, 239 

graphite of the, 75 

hornblende-schist of, 253, 254 

mica-schist of the, 242, 243, 244 

porphyry of, 170 

serpentine of the, 315, 317 

talc, or steatite of the, 354 

zoisite of the, 42 
Fichtenmahle, near Meissen, pitchstone 

of, 224 

Figzan, North Africa, trona of, 59 
Finland, rappakavi (granite) of, 205 

tantalite of, 46 

Flbha, in Saxony, porphyry-breccia of, 

310 
Forfarshire, flagstones of, 300 

phonolite of, 201 

Foya Mountain, in Portugal, foyaite of, 

181 
Framont, in the Vosges Mountains, mi- 

nette of, 173 
France, bituminous substances of, 77 

blue porphyry of, 171 

boracite of. 52 

calcaire grossier of, 282 

flint in the chalk of, 6 

fluor spar of, 69 

granite of, 206 

kersanton of, 175 

malachite of, 60 

menilite of, 278 

polianite of, 65 

schistous trachyte of, 184 

siliceous concretions of, 279 

trachyte of, 186 

Franconia, in New Hampshire, mispickel 
of, 74 

Frankenberg, in the Erzgebirge, granite- 
porphyry near, 213 



GIA 

Franklin, in New Jersey, franklinite of, 

357 
Franzensbad, in Bohemia, polishing slate 

of, 350 

Frauenstein, granite-porphyry of, 214 
Freiberg, epsomite of, 51 

galena of, 70 

gneiss of, 235, 238 

granite-porphyry near, 213 

granular- gneiss of, 239 

mispickel of, 74 

porphyry of, 217, 218 

quartz-schist of, 247 

serpentine near, 317 

wavellite near, 55 
Friedrichsroda, in the Thuringian Forest, 

porphyry of, 217 
Freienhauschen, in the Eifel. trachyte 

of, 191 

Frejus, blue porphyry of. 171 
Fiinfkirchen, coal of, 334 



in the Odemvald, 
kinzigite of, 320 

Gamsigrad, in Servia, timazite of, 156 
Gastein, in the Alps, gneiss of, 239 

titaniferous iron of. 63 

Gata, Cabo de, in Spain, kinzigite of. 320 
Gefrees, in the Fichtelgebirge, chiastolite- 
schist of, 257 

gneiss of. 239 

mica-schist near, 243 
Germany, alunogen of, 50 

amber of, 76 

bituminous mar] of, 273 
shales of, 77, 338 

browncoal clay of, 269 

clay-slate of, 264 

compact marl of, 272 

conglomerate of, 303, 304 

disilicate of protoxide of iron of, 346 

dolomite of, 289, 290 

gypsum of, 293 

hornfels of, 350 

jasper of, 6 

limestones of, 285 

peat of, 328 

porphyrites of, 169 

sandstone of, 299, 300 

septarian clay of, 270 

Geysers, Iceland, soluble quartz in the, 5 
Giant's Causeway, Ireland, analcime of 
the, 30 

basalt of the, 142 

chabasite of the, 31 



INDEX OF LOCALITIES. 



403 



GLA 

Glasgow, coal of, 332 

Gleichenberg, in Styria, trachyte of, 190 

Gloucestershire, Newent sandstone of, 
300 

Goldberg, iu the Fichtelgebirge, gneiss 
of, 239 

Golduiiilil, in the Fichtelgebirge, mica- 
schist near, 244 

Gopfers-Grlin, in the Fichtelgebirge, talc 
of, 354 

Gb'rgeleu, in Hungary, red hematite of, 
343 

Goslar, in the Hartz, pyrites of, 358 

Gothu, lias sandstone of, 299 

Gouverneur, in North America, apatite 
of, 53 

Greenland, colnmbite of, 46 

cryolite of, 69, 353 

graphite of, 75 

on hit e of, 43 

titanite of, 47 

Greifenstein, in Saxony, topaz of, 35 
Grossenhain, granite-gneiss of, 238 
Grosswaltersdorf, near Freiberg, granu- 

lite-gneiss of, 239 

Guipuscoa, in Spain, glaubersalt of, 51 
G umbel, in Bavaria, oltrelite-schist of, 

256 
Gumuchdagh, in Asia Minor, corundum 

of, 351 



HAIDA, in Bohemia, phonolite near, 
200 

Hainersreuth, in the Fichtelgebirge, 
porphyry of, 170 

Hiiinichen, in Saxony, coal of, 333, 
334 

Hammond, zircon of, 41 

Hampshire, clay of, 270 

Hampshire, New, mispickel of, 74 

Hanau on the Maine, semi-opal of, 349 

Handerloo, near Schemnitz, granitic tra- 
chyte of, 184 

Hanover, boracite of, 52 

Hanover, in North America, hornblende- 
schist of, 254 

Hanng, in the Tyrol, eocene coals of, 
330 

Harthau, near Chemnitz, chlorite-schist 
of, 250 

Hartz Mountains, clay-slate of the, 266 

conglomerate of the, 304 

diabase of the, 149 

fluor-spar of the. 351 

galena of the, 70 



HUN 

Hartz Mountains continued 

granitite of the Brocken of the, 
207 

graphite of the, 75 

hausmannite of'the, 64 

labradorite, porphyry of the, 160 

melaphyre of the, 163, 166 

manganite of the, 66 

melaphyre of the, 163 

porphyrite of the, 170 

pyrites of the, 358 

schiller-rock of the Baste in the, 
316 

schiller-spar of the, 19 

wernerite rock of the, 222 
Haslau, near Eger, egeran of, 318 
Hastings, sand of, 299 
Heidelberg, granite near, 207 

granular limestone near, 278 
Herges, in the Thuringian Forest, apha- 

nite of, 159 
Hermsdorf, in the Erzgebirge, porphyry 

of, 218 
Herren-Grund, in Hungary, gypsum of, 

293 

Herrnhut, in Saxony, grannlite of, 231 
Hessen, browncoal of, 330 

dolerite of, 135 

trachyte of, 190 
Hinterbriihl, talc-schist of, 252 
Hitteroe, in Norway, orthite of, 43 

gadolinite of, 43 

Hliniker Valley, in Hungary, millstone- 
porphyry of, 184 

trachyte-porphyry of, 195 
Hoboken, New Jersey, chromic iron-ore 

of, 62 
Hochberg, near Eger, granulite-gneiss 

of, 239 

Hoch-Eppen, porphyry of, 218 
Hof, in the Fichtelgebirge, hornblende- 
schist of, 254 

mica-schist near, 243 

Hbfles, near Eiger, granite-gneiss of, 
238 

Hbgan, phonolite-tufa of, 309 

Hohenelbe, porphyrite near, 170 

Hollennmhle, in Saxony, hypersthenite 
of, 152 

Holstein, boracite of, 52 

Huhnberge, in the Thuringim Forest, 
diorite of, 155 

Huhnerhof, in the Fichtelgebirge, mica- 
schist near, 243 

Hungary, alunite of, 52, 309 

antimony-glance of, 357 



D D 2 



404 



INDEX OF LOCALITIES. 



HUN 

Hungary continued 

basalt of, 187 

carbonate of manganese of, 354 

coal of, 334 

gypsum of. 293 ' 

millstone -porphyry of, 184 

perlite of, 184 

natron of, 59 

nitre of, 55 

oligoclase of, 1 1 

opal of, 8, 309 

perlite of, 196 

pyrites of, 358 

red hematite of, 343 

rhodonite of, 356 

talc-schist of. 252 

timazites of, 161 

trachyte of, 184, 187, 191 

trachyte-porphyry of, 184, 185, 195 
Hutberg, near Dresden, hornbleude-por- 

phyrite of, 172 



TCELAND, apophyllite of, 30 
heulandite of, 33 

obsidian and pumice-stone of, 197 

stilbite of, 33 

siliceous tuff of, 349 

soluble quartz in the geysers of, 5 

trachyte of, 184 

trachyte-porphyry of, 195 
Idria, epsomite of, 51 

Ihlefeld, in the Hartz, hausmannite of, 
64 

manganite of, 66 

Ilfeld, manganese-ores of, 357 

melaphyre of, 165 

porphyrite of, 1 70 

Ilmenau, in Thuringia, braunite near, 
64 

coal of, 333 

ommon felspar of, 10 

'lijausmannite of, 64 
.manganese-ores of, 357 

manganite of, 66 

melaphyre near, 164 

porphyry near, 219 

Ilmensee, near Miask, titaniferous iron 

of, 63 
Indies, East, hislopite of the, 278 

laterite of the, 312 

nitre of the, 55 

nummulitic limestone of the, 283 
Ireland, analcime of, 30 

chabasite of, 31 

cupriferous sandstone of, 300 



KAP 

Ireland continued 

felspar of, 10 

freestone of, 298 

fyalite of, 38 

garnet of, 40 

granite of, 206 

granular limestone of, 278 

limestone of, 278 

phillipsite of, 32 

Ischia, trachytic rocks of, 185 
Iserlohn, galmey of, 356 
Istria, sandstone of, 299 
Itabira, in Brazil, itabirite of, 343 

moorshead rock of, 343 
Itacolumi Mountain, near Villa Rica, 

itacolumite of, 248 
Italy, alum-stone of, 52, 309 

barytes of, 48 

gabbro of, 151 

gypsum of, 293 

marl of, 273 

mellilite of, 42 

nitre of, 55 

sandstone of, 299 

trachyte of, 190 

travertine of, 282 



TAKUBEN, in Bohemia, phonolite of, 

J 200 

Jena, celestine of, 48 

Jersey, New, franklinite of, 357 

vivianite of, 54 

zircon of, 41 
Johanrigeorgenstadtjin Saxony, polianite 

of, 65 



J7 AISERSTUHL, in Brisgau, granular 

-"- limestone of, 278 

Kaiserstuhl, in Baden, pyrochlore of, 

perofskite at, 45 
Kaiserstuhl, sodalite of, 14 

trachyte of, 190 

Kammerbuhl, in Bohemia, basalt of, 

141 
Kaintschatka, siliceous tuff of, 349 

trachydolerite of, 192 

Kandern, on the Schwarzwald, disilicate 
of protoxide of iron of, 346 

Kansas, nacritide of, 244 

Kapnik, in Hungary, carbonite of man- 
ganese of, 354 

Kappellenberg, trachyte of, 190 



IXDEX OF LOCALITIES. 



405 



KAS 

Kasbegk, in the Caucasus, trachyte of, 

188 

Kaschau, in Hungary, opal of, 309 
Katherinenburg, chrysolite of, 39 
K it/iiiittf. in tlia Tlmringian Forest, 

oilstone of, 265 
Kemuath, porphyry near, 218 
Kerbersdorf, near Eger, granite of, 205 
Killan, in Ireland, garnet of, 40 
Killiney Bay, spodumene of, 22 
Kilmacolm, ill Renfrewshire, natrolite of, 

32 

Kilpatrick Hills, scolecite of the, 33 
Kilpatrick, in Dumbartonshire, thoin- 

sonite of, 31 
Kinzig, in the Black Forest, kinzigite 

>f, 320 

Kirkcudbright, zircon of, 41 
Kleinlinden, manganese-ores of, 357 
Klobenstein, in Saxony, garnet rock of 

the, 319 
Klumpsen Mountain, in Oberlausitz, 

diorite of the, 155 
Kongbberg, in Norway, analcime of, 30 

axinite of, 44 

mispickel of, 74 

Koi bach, in the Fichtelgebirge, mica- 
schist near, 243 

Korgon, in the Altai Mountains, porphy- 
rite of, 170 

Kozelniker Valley, near Schemnitz, tra- 
chyte of the, 186 

Krageroe, in Norway, phosphorite of, 
353 

Kremnitz, in Hungary, trachyte of, 184 

Kriebstein, dichroite rock near, 320 

Kronberg, near Erbendorf, porphyry of, 
218 

Krummau, in Bohemia, granulite of, 
231 

Kiinlsbrunnen, in the Siebengebirge, tra- 
chyte of, 191 

Kusstein, in Tyrol, ostraea limestone of 
the, 283 



T AACHERSEE, titanite of, 47 

L* Lagoda Lake, wernerite of the, 222 

Liilni, melaphyre of, 166 

Landshut, in Silesia, melaphyre of, 166 

Langenstriegis, near Freiberg, wavellite 

of, 55 
Lauenstein, in the Erzgebirge, gneiss of, 

239 
Lanrvig, in Norway, zircon-syenite of, 

181 



LYO 

Lauterbach.near Marienberg, granulite- 
gneiss of, 239 

Lehnau, near Kemnath, porphyry of, 
218 

Lehsten, in the Thnringian Forest, roof- 
ing slate of, 264 

Leitha Mountains, conglomerate of the, 
303 

limestone of the, 282 
Lemberg, amber of, 76 
Lengefeld, gneiss of, 238 
Lenne-Gebiet, in Westphalia, porphyrite 

of, 170 

Leschtina, Bohemia, basalt of, 141 
Leukersdorf, in Saxony, porphyry of, 

217 
Lherz, Lake, in the Pyrenees, augite 

rock of the, 149 
Liebenstein, in the Thuringian Forest, 

granite- porphyry of, 213 
Limoges, kaolin of, 13 
Linares, galena of, 70 
Liorant, in Cantal, trachyte of, 186 
Lipari Islands, perlite of the, 184, 

196 

obsidian and pumice-stone of the, 
197 

Lippersdorf. gneiss of, 238 

Liscanera, Lsland of, trachydolerite of, 
192 

Littnitz, in Bohemia, marcasite of, 357 

Lizard's Point, Cornwall, saponite of, 
26 

Llandeilo, flags of, 301 

Llandovery, handstone of, 301 

Lobau, in Saxony, apatite of, 53 

Lobejiin, coal of, 333 

Lochwinnock, in Renfrewshire, thorn- 
son ite of, 31 

Lombardy, trachyte of, 184 

trachyte- porphyry of, 195 
London, clay of, 270 
Lowenherg, melaphyre of, 166 
Lb'wenburg, in the Siebengebirge, trachy- 
dolerite of the rock of the, 192 

Lozere, fraidonite of the, 175 
Ludwigstadt, in the Thuringian Forest, 

carbonaceous schist of, 258 
Ludlow, sandstone of, 301 
Lugano, porphyrite near, 170 
Luneburg, Hanover, boracite of, 52 
Luneville, in France, boracite of, 52 
Luschitz, in Bohemia, mellite of, 77 
Luxembourg, ottrelite of, 27 
Lyons, granite near, 206 

malachite near, 60 



406 



INDEX OP LOCALITIES. 



MAG 

MAGDEBURG, boracite of, 52 
rock-salt near, 352 
Magurka, in Hungary, antimony-glance 

of, 357 
Manebach, in the Thuringian Forest, 

porphyry of, 218, 219 
Maracaibo, in Peru, trona of, 59 
Marebach, aphanite of, 159 
Margola, rock of the summit of the, 164 
Marianna, in Brazil, moorshead rock of, 

343 
Marienburg, in Bohemia, granulite- 

gneiss of, 239 

phonolite of, 200 

Marienberg, in Saxony, porphyrite- 

wacke of, 171 
Markersdorff, in Bohemia, bituminous 

substances of, 77 
Marmaros, in Hungary, red hematite of, 

343 
Massachusetts, chabasite of, 31 

columbite of, 46 

rutile of, 66 

titanite of, 47 

Matlock, in Derbyshire, smithsonite of, 

34 
Mautern, near Mblk, granulite-gneiss of, 

239 
Mayence basin, limestone of the, 282 

marl of the, 273 

sandstone of the, 299 

Megeen, in the Sennethal, barytes of, 

352 
Meissen, in Saxony, granite of, 207 

granular limestone near, 278 

hornblende-schist near, 253 

mica-porphyrite of, 173 

pitchstone of, 225 

quartz-porphyry of, 217 
M?lfi, haiiynophyry of, 141 

leucite of, 186 

Menaccan, in Cornwall, titaniferous iron 

of, 64 

Mendip Hills, smithsonite of, 34 
Menil Montant, Paris, menilite found at, 

8 

Meronitz, in Bavaria, opal of, 349 
Meissner, in Hesse, browncoal of, 330 
Messner Mountain, in Hessen, dolerite 

of, 135 
Mexico, obsidian and pumice-stone of, 

197 

perlite of, 196 

trachyte of, 186 
Miask, pyrochlore of, 45 

titaniferous iron near, 63 



NAS 

Miesbach, Molasse coal of, 330 

Mileschauer, in Bohemia, phonolite of, 
200 

Milo Isles, alunogen of, 50 

Milsburg, on the Rhon Mountain, pho- 
nolite of, 200 

Miltitz, near Meissen, granular limestone 
of, 278 

hornblende-schist of, 253 
Mittelgebirge, in Bohemia, basalt of the, 

142 

phonolite of the, 187, 200 

titanite of the, 47 

Mittweida, in Saxony, granulite of, 231, 

232 
Mohorn, near Freiberg, pitchstone-por- 

phyry of, 225 

porphyry of. 217 

Molina, in Aragon, aragonite of, 58 
Molk, granulite-gneiss near, 239 
Mondhalde, at the Kaiserstuhl, trachyte 

of, 190 
Monfina, Rocca, leucite of, 186 

trachyte doJerite of, 192 
Montabaur, in Nassau, trachyte of, 186 
Montdore, Auvergne, alunite of, 52 
Monte Rosa, granite of, 207 
Montmartre, Paris, siliceous concretions 

of, 279 

Monzoni, pleonaste of, 61 
Moravia, lepidolite of, 355 
Moritzburg, in Saxony, granite of, 207 

granite-gneiss near, 238 
Morocco, nummulitic limestone of, 283 
Mourne Mountains, Ireland, beryl of, 39 

common felspar of, 10 

fayalite of, 38 

topaz of, 35 

Miihlhausen, in Thuringia, peat-beds of, 

328 

Mulatto, porphyritic rocks of, 170 
Miinchberjr, in the Fichtelgebirge, eklo- 

gites of the, 318, 319 

granulite-gneiss near, 239 

hornblende-schist of, 253 
Mursinsk, in Siberia, topaz of, 35 
Mussa Alp, Piedmont, idocrase of, 41 
Muzay, Hungary, alunite of, 52 
Muzo, in Columbia, beryl of, 39 



NAGYAG, in Transylvania, trachyte 
of, 186 
Nassau, palagonite of, 19 

schal stein of, 310, 311 

trachyte of, 186 



INDEX OF LOCALITIES. 



407 



NAT 

Natolia, meerschaum of, 354 
Naxos, corundum of, 351 

emery of, 8 

Negroponte, meerschaum of, 354 
Neurode, in Silesia, hypersthenite of, 
152 

troutstone of, 316 

Neusohl, trachyte-porphyry of the 

Schlossberg ot, 195 
Newcastle, coal of, 332 
Niedermendiir, on the Rhine, basaltic 

lava of, 141 

corundum of, 8 

haUyneof, 15 

Niederschona, near Freiberg, granite- 
porphyry of, 213 

Nile, jasper in the sand of the, 6 

Nischne-Tagilk, in the Ural, dolomite 
of, 289 

Norway, axinite of, 44 

gadolinite of, 43 

magnetic ironstone of, 345 

mispickel of, 74 

norite of, 156 , 

orthite of, 43 

phosphorite of, 353 

porphyrite of, 1 70 

potstone of, 251 

pyrochlore of, 45 

wohlerite of, 46 

zircon of, 41 

zircon-syenite of, 181 
Nossen, sclialstein near, 311 
Nuovo, Monte, leucite of, 185 

trachyte of, 190 



OBERHASLI, in the Alps, gneiss of, 
239 

Oberhohndorf, coals of, 333 
Oberlausitz, in Bohemia, aphanite of, 
161 

diorite of, 155 

phonolite of, 200 

Oberpfalz of Bavaria, apatite of the, 53 
Ober-Pobel, near Alteuberg, greisen of, 

321 
Oberstein, harmotome of, 32 

characteristics of amygdaloid of, 166 

melapliyre near, 164 
Oberweishenthal, in the Erzgebirge, 

actinolite-schist of, 254 
Ochuenkopf, in the Erzgebirge, corun- 
dum of, 351 

granite of, 205 

talc-schist of, 252 



PER 

Odenwald, granite of, 207 

kinzigite of the, 320 

porphyry of the, 2 1 7 
Oederan, in Saxony, minette of, 174 

porphyry of, 218 

Oehrenatock, near llmenau, braunite of, 
64 

manganite of, 66 

Ofen, in Hungary, perlite of, 184 
Oisans, St. Gotthard, axinite of, 44 
Olibano, Monte, near Pozzuoli, trachyte 

of, 190 
Orizaba, Mount, in Mexico, trachyte of, 

186 

Oschatz, bituminous shale of, 338 
Osnabruck, anthracite of, 336 



PALAGONIA, in Sicily, tufa of, 308 

* Pargas, apatite of, 53 

crystals of hornblende and pyroxene 
disseminated in limestone rocks in 
the, 21 

Paria, in Italy, gypsum of, 293 
Paris, glauconite of, 27 

gypsum of, 293 

inenilite. 8, 279,349 

milistofts of the Paris basin, 350 
Paris basin, calcaire grossier of the, 

282 

plastic clay of the, 270 
Partenkirchen, in Bavaria, nodular lime- 
stone of, 280 

Passau, on the Danube, gneiss of, 
239 

granite of, 207 

graphite of, 336 

kaolin of, 14 

Pasto, volcano of, alunogen of, 50 

trachyte of, 186 

Paterno, Monte, near Bologna, barytes 

of, 48 

Pausilippo tufa, 309 
Pelegrin, in Tyrol, porphyry of, 218 
Pennig, in Saxony, granulite of, 231 

hypersthene of, 19 
Pennsylvania, naplitha of, 77 
Pentland Hills, near Edinburgh, por- 
phyry of the, 170 

Perlenhardt, in the Siebengebirge, tra- 
chyte of, 185 
Persia, naphtha of, 77 

nummulitic limestone of, 283 

turquoise of, 54 
Pern, glauberite of, 49 

troiia of, 59 



408 



INDEX OP LOCALITIES. 



PET 

Peterhead, spodumene of, 22 
Phelegrai, Campi, trachytic rocks of the, 

185 
Pic Blanc, Monte Rosa chain, granite of 

the, 207 
Picota Mountain, in Portugal, foyaite of, 

181 
Picton-nob, in North America, specular 

iron of, 343 

Piedmont, idocrase of, 41 
Pike's Peak, in Kansas, nacrite of, 

244 

Pinchincha, andesite of, 192 
Planitz, in Saxony, burnt shale of, 339 

felsite-balls of; 224, 225 
Planschwitz, in Saxony, greenstone-tufa 

of, 310 

Flatten, in Bohemia, polianite of, 65 
Plauenschen-Grund, near Dresden, horn- 

blende-porphyrite of the, 172 

syenite of the, 176, 178, 179 
Plombieres, apophyllite of, 30 

fluor-spar of, 69 

Polwand, near Saalfeld, nodular lime- 
stone of, 281 

Pontellaria, fibrous trachyte of the, 
184 

Pont Jean, in the VosgesliMountains, 
dioriteof, 156 

Ponza Islands, trachyte-porphyry of the, 
184, 195 

Popayan, trachyte near, 186 

Popocatapetl, Mount, trachyte of, 186 

Poppenrent, near Miinchberg, granulite- 
gneiss of, 239 

Potschappel, near Dresden, hornblende- 
porphyrite of, 171 

Portland, sand of, 299 

stone of, 280, 284 
Portugal, foyaite of, 181 

itacolumite of, 249 
Pozzuoli, trachyte near, 1 90 
Predazzo, in the Tyrol, chalcopyrite of, 

74 

granite of, 207 

lievrite of, 37 

uralite of, 18 

Prese, La, in Upper Italy, gabbro of, 
151 

Prussia, Rhenish, zircon of, 41 

Purace, near Popayan, trachyte of, 
186 

Pusu, Island of, in the Ladoga Lake, 
wernerite of, 222 

Puy de Chaumont, near Clermont, tra- 
chyte of, 186 



ROS 

Puy de Dome, domite of the, 184, 188 

oligoclase of, 186 

trachyte of the, 191 
Pyrenees, augite rock of the, 149 



QUIMPER, in Brittany, kersanton of, 
175 
Quito, mud-streams of, 307 



RABEN KLIPPEN, in the Hartz, 
melaphyre of, 166 
Rabenau, in Saxony, gneiss of, 239 
Rabertshausen, in Hessen, trachyte of, 

190 

Radeberg, near Dresden, gneiss of, 238 
Radegrube, near Freiberg, gneiss of, 

238 

Radoboj, in Croatia, sulphur of, 358 
Raibl, in Carinthia, smithsonite of, 34 
Rathlin, Island of, in Ireland, granular 

limestone of, 278 

Raubschlb'sschen, near Weinheim, por- 
phyry of, 219 

Redwitz, in the Fichtelgebirge, gneiss of, 
238 

granite near, 205 

Regenberg, in the Thuringian Forest, 

porphyry of, 217, 218 
Reiohenbach, in Voigtland, alum-schist 

of, 257 
Rhine, basaltic lava of the, 141 

corundum of the, 8 

cypris-slate of the, 266 

hauyne of the. 15 

itacolumite of the, 249 

titanite of the, 47 

Rhb'n Mountain, phonolite of, 200 
Riccamonfina, in the Albanian Moun- 
tains, leucite rock of, 143 
Richenstein, in Silesia, leucopyrite of, 

73 

Rieden, leucite rock of, 143 
Riesengebirge, granitite of the, 207 

malakolite of the, 149 

Rio Tinto, in Spain, pyrites of, 358 
Rocklitz,in the Riesengebirge, malakolite 

of, 149 
Rome, alunite near, 52 

mellilite of, 42 

phillipsite near, 32 
Rosenau, in Hungary, rhodonite of, 

356 
Rosswein, in Saxony, gahbro of, 151 

granulite of, 231 



INDEX OF LOCALITIES. 



409 



ROT 

Rottleberode, in the Hartz, fluor-spar of, 

351 

Rovigo, near Lugano, porphyrite of, 170 
Kozena, in Moravia, lepidolite of, 355 
Rumburg, in Bohemia, granite of, 202, 

207 
Russia, black earth of Southern, 340 

cupriferous sandstone of, 300 

gypsum of, 293 

malachite of, 354 

steppe-limestone of, 282 

volborthite of, 47 

Ruszkberg, in the Banat, coal of, 334 



SAAFELD, nodular limestone near, 
281 

Saalburg, diabase of, 147 

Saarbrucken, Bohemia, alum of, 50 

Sageritz, near Grossenhain, granite- 
gneiss of, 238 

Saidhdiutz, in Bohemia, epsomite of, 51 

Sainte Marie, in the Vosges, kersanite 
of, 176 

Salzburg, beryl of, 39 

Sau-Alp, in Styria, eklogite of the, 318 

SiUtina, diorite of, 155 

S ivoy, aphanite of, 159 

Saxony, alunogen of, 50 

apatite of, 53 

basalt of, 140 

burnt shale of, 339 

chlorite of, 25 

coals of, 333 

conglomerate of, 303 

cordierite of, 44 

dichroite-rock of, 320 

felsite-balls of, 224 

felstone of, 222 

ferreo-liihomarge of, 356 

jiabbro of, 151 

garnet-rock of, 319 

gneiss of, 238, 239 

granite of, 206, 207 

granular limestone of, 277 

granulite of, 231 

green porphyry of, 214 

greenstone-tufa, 310 

hornblende-porphynte of, 171, 172 

liy}>ersthene of, 19 

hypersthenite of, 152 

idocrase of, 42 

kaolin of, 354 

pycnite of, 354 

limestone of, 283 

magnetic ironstone of, 345 



SCH 

Saxony continued 

marcasite of, 73 
"marl of, 273 

mica-schist of, 244 

mica-porphyrite of, 173 

minette of, 174 

nodular or spotted schist of, 257 

occurrence of emery in, 8 

orthite of, 43 

polianite of, 65 

porphyrite-wacke' of, 171 

porphyry of, 217 

porphyry-tuff of, 309, 310 

pyrope of, 4 1 

quartz- porphyry of, 217 

sandstone of, 299 

schorlaceous schist of, 323 

serpentine of, 317 

syenite of, 176, 178, 179 

topaz of, 35, 36 
Scandinavia, limestone of, 286 
Schaumberg, tboleite of the, 138 
Schellerhau, in the Erzgebirge, granite- 
porphyry of, 213 

Schemnitz, in Hungary, agalmatolite 
near, 354 

diorite dL 155 

granithffrachyte of, 184 

perlit*of, 184, 196 

timazifes of, 161 

trachyte of, 184, 186 

trachyte-porphyry of, 195 
Schivelutsch, in Kamtechatka, trachy- 

dolerite of the, 192 
Schlaggenwald, greisen of the, 321 
Schleusenthal, in the Thuringian Forest, 

melaphyre of, 1 64 
Schlossberg, Saxony, basalt of, 140 
Schloitzbachthal, in Saxony, granite of, 

206 
Schmiedefeld, in the Thuringian Forest, 

granite porphyry of, 213 

magnetic ironstone of, 345 

melaphyre near, 167 
Schmollnitz, in Hungary, pyrites of, 

358 

Schneckenstein, in the Voigtland, topaz 
rock of the, 324 

Schneeberg, in the Erzgebirge, granite 
of, 206 

Schneeberg, in the Fichtelgebirge, gra- 
nulite-gneiss of the, 239 

Schneekopf, in the Thuringian Forest, 
porphyry of, 218 

Schneidemiillersberg, near Ilmenau, me- 
laphyre of, 164 



410 



INDEX OF LOCALITIES. 



SCH 

Schonfeld, in the Erzgebirge, anthracite 

of, 336 
Schwarzbach, in the Fichtelgebirge, 

chlorite-schist of, 250 
Schwarzenbach, in the Fichtelgebirge, 

mica-schist of, 242 
Schwarzenberg, in Saxony, garnet-rock 

near, 319 
Sehwartzenberg, in the Erzgebirge, 

gneiss of, 238 

talc-schist of, 252 
Schwarzenfels, in the Erzgebirge, quartz- 
breccia of, 305 

Schwarzwald, common quartz in the 
sandstone of, 6 

disilicate of protoxide of iron of the, 
346 

Scotland, analcime of, 39 

basalt of, 142 

cannel or parrot-coal of, 332 

carboniferous ironstone, or blacfcband 
of, 346 

hypersthenite of, 152 

laumontite of, 32 

natrolite of, 32 

phonolite of, 201 

porphyry of, 170 

prehnite of, 31 

sandstone of, 300 

thomsonite of, 31 

titanite of, 47 

Seegeberg, in Holstein, boracite of, 52 
Seerenbach, near Tharand, gneiss of, 239 
Seisser Alp, analcime of the, 30 

inelaphyre of, 163 
Servia, timazite of, 156 

Shelburne, in Massachusetts, rutile of, 66 
Shropshire, stiper stones of, 301 
Siberia, epsomite of, 51 

malachite of, 60 

topaz of, 35 
Sicily, analcime of, 30 

gypsum of, 293 

palagonite of, 19 

tufa of, 308, 309 
Siebengebirge, trachyte of the, 186, 188, 

191 

trachydolerite of the, 192 
Siebei'.helm,near Freiberg, serpentine of, 

317 

gabbro of, 151 
Siegburg, dolerite of, 135 
Siegen, polianite of, 65 

Silesia, corundum in the granite of, 8 

galena of, 70 

hypersthenite of, 152 



STE 

Silesia continued 

leucopyrite of, 73 

melaphyre of, 164, 166 

native coke or anthracite of, 334 

pebbles of, 103 

porphyry of, 219 

smithsonite of, 34 

Silthal in Transylvania, coal of, 334 
Skiddaw, in Cumberland, chiastolite- 

schist of, 257 

Skutsch, in Bohemia, amber of, 76 
Skye, Isle of, heulandite of, 33 

hypersthene of, 19 

hypersthenite of, 152 

labradorite of the, 1 1 

Slatoust, in the Ural, perofskite of, 45 
Solenhofen, in Bavaria, slaty limestone 

of, 281 
Somma, Monte, anorthite in the lavas 

of, 12 

leucite rock of, 143, 186 

meionite of, 42 

spinel of, 61 

Sonnenberg, in Bohemia, gneiss of, 238 
Sonnerberg, in the Thuringian Forest, 

pencil-slate of, 264 

Soos, in Bohemia, polishing slate of, 350 
Spain, aragouite of. 58 

cinnabar of, 358 

galena of, 70 

glauberite of, 49 

glaubersalt of, 51 

itac.lumite of. 249 

kinzigite of, 320 

nitre of, 55 

pyrites of, 358 
Spechtshausen, in Saxony, felsite-balls 

of, 224 

pitchstone-porphyry of, 225 
Staffa, basalt of, 142 

scolecite of, 33 
Staffordshire, coals of, 332 

peldon of, 298 

St. Agnes, Cornwall, vivianite of, 54 
Staniren Alf, in Styria, anthracite of, 

336 
Stassfurt, near Magdeburg, boracite of, 

52 
St. Austell, Cornwall, common quartz 

of, 5 

Steindoif, in the Banat, coal of, 334 
Steingrun, near Eger, gneiss of, 239 
Steinhaide, in the Thuringian Forest, 

sandstone of, 297 

Stemzelberg, in the Siebengebirge, tra- 
chyte of,' 186, 188, 191 



INDEX OF LOCALITIES. 



411 



ST. 

St. Gall, pebbles of, 102 
St. Gotthard, axinite of, 44 

ad ul aria at, 9 

corundum of, 8 

fluor-spar of, 69 

gneiss of, 239 

gypsum of, 292, 293 

paraeonite-schist of, 244 

tourmaline near, 37 

St. Loretta, in the Leitha Mountains, 

conglomerate of, 303 
Stockholm, oligoclase of, 11 
Stolpen, basalt near, 140 
St. Ouen, Faris, siliceous concretions of, 

279 
Strassberg, in the Hartz, fluor-spar of, 

351 
Strassfurt, near Magdeburg, rock-salt 

of, 352 

boracite of, 353 
Stromboli, dolerite of, 137 

trachydolerite of, 192 
Stroutian, Ar^yleshire, titanite of, 47 
St. Stephen's, in Cornwall, kaolin of, 13 
Styria, anthracite of, 336 

eklogite of, 318 

fullers' earth of, 356 

graphite of, 75 

paragonite of, 58 

trachyte of, 190 

St. Yiieix, near Limoges, kaolin of, 

13 
Supgsville, in North America, orbitoidal 

limestone of, 283 
Sussex, Weald clay of, 270 
Swabia, barytes of, 48 

celestine of, 48 

clays of, 270 

dolomite of, 289, 290 

marl of, 273, 274 

sandstone of, 299 
Swarzenbertr, Saxony, idocrase of, 42 
Sweden, automolite of, 61 

eulisite of, 319 

felsite-schist of, 222 

hsulandite of, 33 

gadolinite of, 43 

hypersthenite of, 152 

idocrase of, 41 

magnetic ironstone of, 345 

mica-schist of, 242 

porphyrite of, 170 

pyrites of, 358 

spodumene of, 22 

stilbite of, 33 

tantalite of, 46 



THU 

Sweetwater River, Rocky Mountains, 
trona of, 59 

Switzerland, common quartz in the gra- 
nites of, 6 

glarus-slate of, 266 

gypsum of, 293 

sandstone of, 299 

staurotide of, 36 

Syra, island of, eklogite of the, 318 



TABARZ, in the Thuringian Forest, 
aphanite of, 159 

Takli, in the East Indies, hislopite of, 
278 

Tannebergsthal, in the Erzgebirge, por- 
phyry of, 217 

Tarapaca, in Peru, glauberite of, 49 

Tarnowitz, in Silesia, galena of, 70 

galmey of, 356 

smithsonite of, 34 

Taunus, sericite-schist of the, 256 
Telkebanya, in Hungary, perlite of, 184 

perlite of, 196 

Teneriffe, peak of, obsidian and pumice- 
stone of the, 197 

trachydolerite of, 192 

trachyte of the, 186, 188 

tufa of, 309 

Ternuay, in the Vosges, aphanite of, 

160 

Test-hen, variety of diabase of, 148 
Tet.schen, in Bohemia, phonolite, near, 

200 
Teufelsstein, in Saxony, garnet- rock of 

the, 319 
Tharand, in Saxony, felsite-balls near, 

224 

felstone near, 222 

gneiss of, 239 

granite near, 206 

marcasite of, 73 

quartz-porphyry of, 217 
Thibet, borax of, 53 

Thuringian Forest, aphanite of the, 159 

carbonaceous schist of the, 257 

conglomerate of the, 303, 304 

diorite of the, 155 

dolomite of the, 290 

dolomitic sand of the, 290 

granite-porphyry of the, 207, 213 

hau.smannite of the, 64 

kaolin-sandstone of the,297 

magnetic iron-stone of the, 345 

manganite of the. 66 

marl of ihe, 274 



412 



INDEX OP LOCALITIES. 



THU 

Thuringiah Forest continued 

melaphyre of the, 163, 164 

mellite of the, 77 

miacytan clay of the, 270 

mica-porphyrite of the, 173 

oilstone of the, 265 

peat-beds of the, 328 

pencil-slate of the, 264 

porous limestone of the, 281 

porphyries of the, 217, 218, 219 

quartz-porphyry of the, 217 

quartz-porphyries and mica-porphy- 
ries of the, 187 

roofing-slate of the, 264 

shale of the, 267 

white or grey sandstone of the, 300 
Tokay, in Hungary, perlite of, 196 

trachyte of, 184 

Tolfa, La, Italy, alum-stone of, 309, 
352 

trachyte of, 184 

trachytic rocks of, 185 

Tolima, in South America, trachyte of, 

186 
Toluca, Mount, in Mexico, trachyte of, 

186 

Tolz, Molasse coal of, 330 
Totnn Fjeld, in Norway, orthite of, 

43 
Transylvania, coal of, 334 

porphyry of, 219 * _ 

pyrites of, 358 

sandstone of, 296 

syenite of, 179 

trachyte of, 186, 191 

wohlerite of, 46 

Trebendorf, near Eger, granite of, 205 
Treyalgan, Cornwall, tourmaline of, 38 
Triebisch Thai, near Meissen, pitch- 
stone of the, 225 
Trinidad, asphalte of, 77 

bitumen of, 337 

Trostburg, in Tyrol, porphyry of, 218 
Tumilla, apatite of, 53 
Tunaberg, in Sweden, eulisite of, 319 
Tunguragua, in South America, tra- 
chyte of, 186 

Turkey, nephrite and jade of, 18 
Tuscany, trachyte of, 184 
Tyrol, amphilogite-schist of the, 244 

chalcopyrite of the, 74 

crystals of hornblende and pyroxene 
disseminated in the limestone rocks 
in the, 21 

eocene coals of the, 330 

granite of the, 207 



VIT 

Tyrol continued 

granitite of the, 207 

hypersthene in the, 19 

lievrite of the, 37 

melaphyre of the, 164 

oligoclase of the, 11 

ostrsea limestone of the, 283 

porphyrites of the, 1 69 

porphyritic rocks of the, 170 

porphyritic syenite of the, 178 
porphyry of the, 218 

predazzite of the, 289 
staurotide of the, 36 

tonalite of the, 207 

tufas of the, 310 

TTNITED STATES,alunogenof the, 50 
U Unst, Island of, chromic iron-ore of 

the, 62 
Ural Mountains, beresite of the, 207 

dolomite of the, 289 

itacolumite of the, 249 

miascite of the, 180 

oligoclase- porphyry of the, 160 

perofskite of the, 45 

talc-schist of the, 252 

zircon of the, 41 

Uto, in Sweden, apophyllite of, 30 

spodumene of, 22 

yALENCIA, in Aragon, aragonite of, 

Velay, trachyte of, 184 

Vesuvius, garnet in the lavas of, 40 

hematite of, 63 

idocrase in old lavas of^ 41 

leucite of, 186 

leucite rock of, 143 

magnetic pyrites in the lavas of, 
72 

natron of, 59 

thomsonite in the lavas of, 31 
Vienna basin, tile- or brick-earth of the, 

269 

Vienna-sand, 299 
Viesembach, in the Vosges Mountains, 

kersanite of, 176 
Villa Rica, itacolumite of, 248 

moorshead rock of, 343 

Villa Rubia, in Spain, glauberite of, 

49 
Visena Valley, in Tyrol, porphyritic 

syenite of the, 178 
Viterbo, trachyte of, 184 



INDEX OF LOCALITIES. 



413 



VOI 

Voigtland, chiastolite-schist of, 257 

alum-schist of. 257 

diabase of, 1 49 

granite-gneiss of, 238 

topaz rock of. 324 

Volturara, near Melfi, haiiyne, of, 15 
Vosges, andesine of the, 1 1 

apatite of the, 1 60 

conglomerate of the, 303 

diorite of the, 156 

mica-diorite of the, 179 

niinette of the, 173 

kereanite of the, 176 

sandstone of the, 300 

Vulture, near Melfi, haiiynopbyry of, 
141 

extinct volcano of, leucite of the, 
186 



WACHENBERG, in the Odenwald, 
porphyry of, 217 
Waldenberg, in Silesia, porphyry of, 219 

native coke or anthracite of, 334 

pebbles of, 103 

Waldheim, in Saxony, serpentine of, 317 
Waldshut, fluor-spar of, 69 
Wales, oilstone of, 265 

roofing and pencil-slate of, 264 
Walkberg, in Bohemia, basalt of, 141 
Walpenruth, in the Fichtelgebirge, mica- 
schist near, 243 

Warwick, in America, rntile of, 66 
Wechselburg, in Saxony, gneiss of, 239 

nodular or spotted schist of, 257 
Weigmannsdorf, in Saxony, gneiss of, 

238 

Weinheim, porphyry near, 219 

Weisig, near Dresden, hornblende-por- 
phjrite of, 172 

Weissenborn, gneiss of, 238 

Weissenfels, in Thuringia, kaolin-sand- 
stone of, 297 

Weissritzthal, in Saxony, minette of the, 
174 

Wenlock, sandstone of, 301 

Weser Mountains, bituminous shale of 
the, 338 

Weslau, near Redwitz, granite of, 205 

Westmoreland, limestone of, 285 

Westphalia, conelomerate of, 303 

Hils clay of, 270 

Hils sandstone of, 299 

marl if, 273 

porphyrite of, 170 

serpulite limestone of, 284 



ZOB 

Wettin, coals of, 333 

Weiford, garnet of, 40 

Whitby, dogger sandstone of, 299 

Wicklow, freestone of, 298 

Wiegersdorff, black melaphyre of, 166 

Wiener Neustadt, granulite of the 

Glocknitzer Schossberg at, 231 
Wiersberg, in the Fichtelgebirge, chlo- 

rite-schist of. 250 
Wight, I.sle of, glauconite of the, 27 
Wilsdruff, in Saxony, hornblende-por- 

phyriteof, 171 
Winterstein, in the Tlmringian Forest, 

quartz-porphyry of, 217 
Wittichen, in the Black Forest, kinzigite 

of, 320 

Wolkenburg, in the Siebengebirge, tra- 
chyte of, 186. 188, 191 
Wiirtemburg, bituminous shale of, 338 
Wurzen, in Saxony, green porphyry of, 

214 



yORK, New, rutile of, 66 
-*- Yorkshire, amber on the coast of, 
76 

dogger sandstone of, 299 

dolomite of, 299 



7AWHAUS, in Saxony, anthracite of, 
fl 336 

granular limestone of, 277 

in the Erzgebirge, mica-schist near, 
244 

Zbirow, in Bohemia, wavellite of, 55 
Zealand, New, nephrite and jade of, 18 

olivine of, 39 

siliceous tuff of, 349 

Zebernick, in Hungary, talc-schist of, 
252 

Zell, in the Fichtelgebirge, serpentine of, 
317 

Zelle, near Nossen, schalstein of, 311 

Zermatt, perofskite of, 45 

Ziegenrucken, near Hohenelbe, porphy- 
rite of, 170 

Zillerthal, in the Tyrol, amphilogite- 
schist of 244 

apatite of. 53 

Zimpan, in Mexico, perlite of, 196 
Zinnwald, in the Erzgebirge, greisen of 

the, 321 

Zittau, in Saxony, burnt shale of, 339 
Zoblitz, in the Erzgebirge, serpentine of, 

317 



414 



INDEX OF LOCALITIES. 



zsc 

Zschopau, the, in Saxony, granulite of, 

231 

Zweibrucken, harmotome of, 32 
Zwickau, in Saxony, burnt shale of, 

339 
coals of, 333 



ZWI 

Zwickau continued 

felsite balls of, 224, 225 

ferreo-lithomarge of, 356 

mica-porphyrite of, 173 

porphyry of, 218 

pycnite of, 354 



GENERAL INDEX. 



ACI 

4CIDIC rocks, 128 
ft- Actinolite, characteristics and oc- 
currence of, 17 
classy, 17 
Adularia, characteristics and occurrence 

of, 9, 2C3, 207 
Agalmatolite, or figure-stone, occurrence 

of, 354 
Agate, characteristics and occurrence of, 

6,351 
Alabaster, characteristics and occurrence 

of, 49 

Albine. See Apophyllite, 30 
Albite, characteristics and occurrence 

of, 10 
Allanite, characteristics and occurrence 

of. 43 

Allogovite, 142 
A hi iand hie. 40 
Alpinite, 239 
Alum, characteristics and occurrence of, 

50 

Aluminum, oxides of, 5 
Alum-schist, 257 
Alumstone, 51, 309, 352 
Alunite, characteristics and occurrence 

of, 51, 352 
Alunogen, characteristics and occurrence 

of, 50 
Amber, characteristics and occurrence 

of, 76 
Amethyst, colouring matter of, 6 

occurrence of, 350 
Amphibole. See Hornblende, 16 
Amphilogite-schist, 244 
Amygdaloid, the term explained, 97 

of Oberstein described, 166 
Analcime, characteristics and occurrence 

of, 29 

Analcymite, 138 
Auamesite, 134 
Andalusite section of minerals,'34 

characteristics and occurrence of, 34 
Andesine, composition and occurrence 

of, 11 



BAR 

Andesite, 185, 191 

Anhydrite, characteristics and occur- 
rence of, 48, 290, 293 

Ankerite, characteristics and occurrence 
of, 57, 355 

Anorthite, characteristics and occur- 
rence of, 12 

Anthracite, characteristics and occur- 
rence of, 335 

Anthraconite, 277 

Antimony-glance, occurrence of, 357 

Apatite, characteristics and occurrence 
of, 53 

Aphanite, characteristics and occurrence 
of, 157 

varieties in texture of, 158 

in composition of, 159 

Aplite, or semi-granite, 207 

Aplome garnet, 40 

Apophyllite, characteristics and occur- 
rence of, 30 

Aragonite, characteristics and occur- 
rence of, 58, 353 

Arenaceous, the term explained, 97 

Argillaceous fonnationsof rocks,! 1 5, 263 

Arsenical pyrites, 357 

Arseniurets, 69 

Arsenopyrite, characteristics and occur- 
rence of, 73 

Asbestus, occurrence of, 18 

Asphalte, characteristics of, 76 

localities of, 77 

Augite section of minerals, 16 

characteristics and occurrence of, 19, 
148 

Automolite, 60 

Axinite, characteristics and occurrence 
of, 43 



T) AGSHOT sand, 299 

-D Baryt-harmotome, characteristics 

and occurrence of, 32 
Barytes, characteristics and occurrence 

of 47, 352 



416 



GENERAL INDEX. 



BAS 

Basalt, characteristics of, 138 

varieties in texture of, 140 

in composition of, 141 

Basaltic rocks, characteristics of, 132 
Basic rocks, 128 

composition of, 129 

Bath-stone, 280 

Bedding of rocks, 108 

Beresite, 207 

Beryl, characteristics and occurrence of, 

39 
Biotite, characteristics and occurrence 

of, 23 

Bitter-spar, characteristics of, 57 
Bitumen and mineral pitch, character- 
istics and occurrence of, 76, 337 
Bituminous shale, 338 
Blende, characteristics and occurrence 

of, 70 
Bog, 327 
Bog-ore, 342 
Bole, occurrence of, 355 
Bologna-spar, or Bologna-stone, 48 
Boracite, characteristics and occurrence 

of, 52, 353 
B orates, 52 
Borax, characteristics and occurrence 

of, 52 

Boulders, formation of, 102, 304 
Braunite, characteristics and occurrence 

of, 64 

Braunstein, 64 
Breccia, the term explained, 97 

characteristics and occurrence of, 
304, 308 

geological varieties of, 305 
Breunnerite, characteristics of, 57 
Browncoal, or lignite, characteristics 

and occurrence of, 329 

varieties of, 329 
Brown-spar, characteristics of, 57 



C\ AEN stone, 280 

^ Calaite, characteristics and occur- 
rence of, 54 

Calarnine, 58 

Calamite, characteristics and occurrence 
of, 17 

Calcareous spar, 57 

Calciphyre, 278 

Calcite, 57 

Calcspar, characteristics and occurrence 
of, 57 

Cannel coal, 332 

Carbonaceous group, 324 



CLA 

Carbonaceous group continued 

varieties of composition, 324 f 

review of the important coal or- 

mations, 326 
Carbonates, 56 

anhydrous, 56 

hydrous, 59 
Carlsbad twins, 10 

Cassiterite, characteristics and occur- 
rence of, 65 

Celestine, characteristics and occurrence 
of, 48 

Cerine, characteristics and occurrence 
of, 43 

Cerusite, 70 

Ceylonite, characteristics and occur- 
rence of, 60 

Chabasite, characteristics and occur- 
rence of, 30 

Chalcedony, composition of, 6 

Chalcopyrite, characteristics and occur- 
rence of, 74 

Chalk, red, 62 

black, 257 

white, 280 

glauconitic, 280 

upper and lower, 283 
Chert, characteristics of, 7, 350 

formation of, 350 

black, 350 

Chiastolite, characteristics and occur- 
rence of, 34 

Chiastolite-schist, 256 

Chlorides, 67 

Chlorite, characteristics and occurrence 
of, 24 

Chlorite-schist, and potstone, character- 
istics and occurrence of, 250 

varieties of, 250 

Chromic iron-ore, characteristics and 
occurrence of, 62 

Chromite, 62 

Chrysolite, characteristics and occur- 
rence of, 38 

Cinnabar, characteristics and occurrence 
of, 71, 358 

Cipollmo, 277 

Clay, characteristics and occurrence of, 
269 

varieties and composition, 269 

geological terms for certain clays, 269 
Clay-ironstone, 58 

Clay-slate, characteristics and occur- 
rence of, 263 

varieties in texture of, 264 

varieties in composition of, 265 



GENERAL INDEX. 



417 



CLA 

Clay -slate continued 

geological varieties of, 266 
Clays, occurrence of, 14 

burnt, characteristics and occurrence 
of, 338 

varieties of, 339 

Claystone and hardened clay, character- 
istics and occurrence of, 270 
Clink.^tone, 198 
Clinochlore, 25 
Coal formations, 117 

common, black coal, pit-coal, cha- 
racteristics and occurrence of, 331 

varieties of, 332 
Colophonite, 40 
Columbates, 45 

Coluinbite, characteristics and occur- 
rence of, 46 

Comptonite, characteristics and occur- 
rence of, 31 

Cone-in-cone, 99 

Conglomerate, the term explained, 97 

formations, 1 1 6, 302 

characteristics and occurrence of, 
302 

Copper-ore, blue, 60 

Copper-pyrites, characteristics and oc- 
currence of, 74 

Coprolite beds, composition and occur- 
rence of, 340 

Coral rag, 284 

reefs, 282 
Cordierite, 44 
Cornbrash, 284 

Corundum, characteristics and occur- 
rence of, 8, 351 

Crichtonite, characteristics and occur- 
rence of, 63 

Cryolite, characteristics and occurrence 
of, 69, 353 



T\AMOURITE, character of, 23 

Davyne, characteristics and occur- 
rence of, 16 

Delessite, 25 

Dendrites, formation of, 100 

Desinine, characteristics and occurrence 
of, 33 

Diabase, characteristics and occurrence 
of, 146 

varieties in texture of, 147 

in composition of, 148 
Diallage, composition of, 19 

rock, 150 

Diallogite, occurrence of, 354 



EUR 

Diamond, 336 

Dichroite, characteristics and occur- 
rence of, 44 

rock, characteristics and occurrence 
of, 320 

Diopside, characteristics of. 18 
Diorite, characteristics and occurrence 
of, 153 

varieties in texture of, 155 
Disthene, characteristics and occurrence 

of, 36, 318 
Dolerine, 252 
Dolerite, characteristics of, 134 

analysis of, 135 

varieties in texture of, 136 

variety in composition of, 136 
sub varieties ot texture of, 137 

Dolomite, characteristics and compo- 
sition of, 57, 274, 287 

varieties in texture of, 288 
in composition of, 289 

geological varieties of, 289 
Dnnite, 39 

Dyke, the term explained, 108 



"pAGLE-stone, 295 
*-* Earth, black, composition and oc- 
currence of, 340 
fullers', 355 
- yellow, 356 
Egeran, characteristics and occurrence 

of, 41 
Eklogite, characteristics and occurrence 

of, 318 
Elsoolite, characteristics and occurrence 

of, 16 

Elaterite, 77 
Elements, native, 74 
Elvanite, 214 
Emerald, characteristics and occurrence 

of, 39 

Emery, occurrence of, 8 
Epidosite, occurrence of, 35, 355 
Epidote, characteristics and occurrence 

of, 42 

Epsom salt, 51 
Epsom ite, characteristics and occurrence 

of, 51 

Erratic blocks, 304 
Esbonite, 40 
Eukrite, 148 
Eulisite, characteristics and occurrence 

of, 319 

Euphotide, 151 
Eurite, 220 







418 



GENERAL INDEX. 



FAH 

TUHLUNITE, occurrence of, 44 

Felsite rock, 220 
Felsite-schist, 220 
Felspar, characteristics of, 8 

orthoclastic, 9 

varieties of colour and lustre, 9 

plagioclastic, 10 

some aids for distinguishing the 
felspar species, 12 

Felspar-porphyry, 169 
Felstone, characteristics and occurrence 
of, 220 

varieties of, 222 
Ferreo-lithomarge, 356 
Figure-stone, 354 

Flint, colouring matter of, 6 

where found, 6 

chalk-flints, 283 

Fluor, Fluor-spar, characteristics and 
occurrence of, 68, 351 

Fluorides, 67 

Foyaite, characteristics and occurrence 
of, 181 

Fragmental rocks, 294 

Fraidronite, characteristics and occur- 
rence of, 174, 175 

Fullers' earth, composition and occur- 
rence of, 355 

Fyalite, 38 



p ABBRO, composition of, 150 
^J varieties in composition of, 1 50 
Gadolinite, characteristics and occur- 
rence of, 43 
Gahnite, 60 
Galena, characteristics and occurrence 

of, 69, 357 
Galmey, 33, 58 

composition and occurrence of, 356 
Garnet section of minerals, 38 

characteristics and occurrence of, 
39 

varieties, 40 

Garnet rock, characteristics and occur- 
rence of, 319 

Glaciers, formation of, 348 

Glauberite, characteristics and occur- 
rence of, 49 

Glaubersalt, characteristics and occur- 
rence of, 51 

Glauconite, characteristics and occur- 
rence of, 27 

Gneiss, characteristics and occurrence 
of, 232 

varieties of, 234 



HEM 

Gneiss continued 

varieties in texture of, 238 

in composition of, 239 

Gneissite, 234 

Gb'thite, 67 

Grammatite, characteristics and occur- 
rence of, 17 
Granite, characteristics of, 203 

varieties in texture of, 205 

occurrence of, 208 

proposed new division of, 209 
Granitic porphyry and syenitic por- 
phyry, 212 

characteristics and occurrence of, 2 1 2 
Granitite, 207 

Granitone, 150 

Granulite, Leptynite, characteristics and 
occurrence of, 229 

varieties in texture of, 231 
Graphite, characteristics and occurrence 

of, 75, 336 

Gravel, formation of, 102 
Green earth, occurrence of, 19 
Greenovite, 47 
Greenstones, characteristics, varieties, 

and occurrence of, 145 
Greisen, essential ingredient of, 23 

as a variety of granite, 207 

characteristics and occurrence of, 32 1 
Gritstone, 295 

Grossularite, 40 

Guano, composition and occurrence of, 

339 
Gypsum, characteristics and occurrence 

of, 49, 274, 290 

varieties in texture and compo- 
sition of, 291 



TTALLEFLINTA, 220, 222. 

-*--* Halunogen. characteristics and oc- 
currence of, 50 

Harmotome, characteristics and occur- 
rence of, 32 

Hastings sand, 299 

Hausmannite, characteristics and oc- 
currence of, 64 

Haiiyne, characteristics and occurrence 
of, 15 

Hatty nophyry, 141 

Hematite, characteristics and occurrence 
of, 62 

brown, 67, 341 

varieties in texture of, 341 

in composition of, 342 

red, 342 



GENERAL INDEX. 



419 



HEM 

Hematite continued 

red, varieties in texture and compo- 
sition, 343 

Hemitrene, 278 

Heulandite, characteristics and occur- 
rence of, 33 

Hislopite, 278 

Hohlspath, characteristics and occur- 
rence of, 34 

Hone, 265 

Honey-stone, 17 

Hornblende, characteristics and occur- 
rence of, 16, 17 

varieties of, 16 

differences between hornblende and 
pyroxene, 20 

Horublende-porphyrite, 171 
Hornblende-schist, and Hornblende-rock, 
characters and occurrence of, 253 

varieties in texture of, 253 

variety in composition of, 254 
Hornstone, characteristics of, 7, 350 

occurrence of, 350 

Hyacinth, characteristics and occurrence 
of, 41 

Hyalite, colourless, where found, 8 

Hypersthene, characteristics and occur- 
rence of, 19 

Hyperstheuite, composition of, 152 



TCE, as a rock, formation of, 347 
-*- glaciers, 348 
underground ice-strata of Siberia,349 
Ichthyophthalmite, characteristics and 

occurrence of, 30 
Idocrase, characteristics and occurrence 

of, 41 
Igneous rocks, 127 

composition of, 129 

varieties of, 129 

basic, 131 

volcanic, 131 

plutonic, 144, 201 

acidic, 182 

volcanic, 182 

observations on the processes of 

igneous rock-formation, 361 
Ilmenite, characteristics and occurrence 

of, 63 
Ilvaite, characteristics and occurrence 

of, 36, 356 
lolite, characteristics and occurrence of, 

44 

Iron-earth, blue, characteristics and oc- 
currence of, 54 



LAS 

Iron, spathic, 57, 345 

oxydulated, 61 

specular, 62, 344 

red, 62 

fibrous, 62 

scaly, 62 

froth, 62 

micaceous, 62 

titaniferous, 63 

pyrites, 72 
white, 72 

hydrous, 72 

disilicate of protoxide of iron, 346 
Iron-ore, sparry, 57 

magnetic, 61, 344 

red, 62 

titanic, 63 

brown, 67 

Iron-stone group of rocks, 340 

geological varieties of, 340, 341 
Itabirite, 343 

Itacolumite, characteristics and occur- 
rence of, 247 

varieties of, 248 



JASPER, characteristics and occur- 

J rence of, 6, 351 

Jenite, characteristics and occurrence of, 

36 

Jointed structure of rocks, 103 
Jointing, various kinds of, 103-105 



KAOLIN, characteristics and occur- 
rence of, 18, 354 

Karren, or Earrenfelder, 101 

Karstenite, characteristics and occur- 
rence of, 48 

Kersantite, characteristics and occur- 
rence of, 175 

Kersanton, characteristics and occur- 
rence of, 175 

Killinite, composition of, 22 

Kinzigite, characteristics and occurrence 
of, 320 

Kyanite, characteristics and occurrence 
of, 36 



T ABRADORITE, characteristics and 

" occurrence of, 1 1 

Lapis lazuli, characteristics and occur- 
rence of, 15 

Lasionite, characteristics and occurrence 
of, 54 



E S 2 



420 



GENERAL INDEX. 



LAS 

Lasurite, characteristics and occurrence 
of, 60 

Laumontite (Laumonite), characteristics 
and occurrence of, 32 

Lava, the term explained, 96 

Lead-ore, blue, characteristics and oc- 
rence of, 69 

Lepidolite, characteristics and occur- 
rence of, 23, 355 

Leucite, characteristics and occurrence 
of, 15. 142 

varieties in texture of, 143 
Leucopyrite, characteristics and occur- 
rence of, 73 

Liebnerite, occurrence of, 44 

Lievrite, or Ilvaite, characteristics and 
occurrence of, 36, 356 

Lignite, 329 

Lime-mesotype, characteristics and oc- 
currence of, 33 

Limestone formations, 116, 274 

characteristics and occurrence of, 
276 

varieties in texture of, 277 

geological varieties of, 282 
Limonite, characteristics and occurrence 

of, 67 

Listwenite, 252 

Lithia-mica, characteristics and occur- 
rence of, 23, 355 

Lithionite, characteristics and occur- 
rence of, 23, 355 

Lithomarge, occurrence of, 355 

Loam, 269 

Lode, the term explained, 108 

Lydian stone, Lydite, black chert, com- 
position and occurrence of, 350 



MAGNESIA - MICA, characteristics 

"- and occurrence of, 23 

Magnesite, characteristics and occur- 
rence of, 57, 355 

Magnetic iron-ore, Magnetite, character- 
istics and occurrence of, 61, 344 

varieties in texture and compo- 
sition of, 344 

Magnetic pyrites, characteristics and 
occurrence of, 71 

Magnetite, 61 

Majolica, 283 

Malachite, characteristics and occur- 
rence of, 59, 354 

Malakolite, occurrence of, 19, 149 

Manganese-ores, occurrence of, 356 

Manganese-spar, occurrence of, 356 



MIN 

Manganite, characteristics and occur- 
rence of, 66 

Marcasite, or hydrous pyrites, character- 
istics and occurrence of, 72 

Margarodite, characteristics of, 23 

Marl formations, 116, 271 

Marl, characteristics and occurrence of, 
272 

varieties in texture and composition 
of, 272 

Marlstone, 272, 274 

Meerschaum, characteristics and occur- 
rence of, 28, 354 

Meionite, 42 

Melanite, 40 

Melaphyre, characteristics and occur- 
rence of, 162 

Mellilite, 42, 77 

Mellite, characteristics and occurrence 
of, 77 

Melinite, occurrence of, 356 

Menilite, 349 

Menachine-ore, 46 

Mesitine-spar, characteristics of, 57 

Miarolite, 206 

Miascite, characteristics and occurrence 
of, 180 

Mica section of minerals, characteristics 
of, 22 

binaxial mica, 22 

hexagonal or uniaxial, 23 
Mica-diorite, 157, 179 
Mica-porphyrite, or Micaceous Porphyry, 

172 

Mica-schist, characteristics and occur- 
rence of, 241 

varieties in texture and composition 
of, 243 

Mica-schist, argillaceous, characteristics 
and occurrence of, 254 

varieties in texture of, 255 

in composition of, 256 

Mica-trap rocks, 173 

Mica-trap, characteristics and occur- 
rence of, 174 

Microcline, characteristics and occur- 
rence of, 9 

Mimetisite, 70 

Minerals, 1 

the principal minerals, 2 

the accessory ingredients of rocks, 2 

' Paragenesis ' of minerals, 3 

mode of classification adopted, 3 

chemical symbols used, 4 

minerals as rocks, 347 

mineral veins and veins of ore, 392 



GENERAL INDEX. 



421 



MIN 

Minette, characteristics and occurrence 
of, 174 

Mirabilite, characteristics and occurrence 
of, 51 

Mispickel, characteristics and occurrence 
of, 73 

Mnja, 307 

Moorshead rock, 343 

Mountain leatlier, 18 

Muriacite, characteristics and occur- 
rence of, 48 

Muscovite. See Potash-mica 



VTACRITIDE, 244 

-L' Naphtha, characteristics and occur- 
rence of, 76 
Natrolite, characteristics and occurrence 

of, 31 
Natron, characteristics and occurrence 

of, 59 
Nepheline, characteristics and occurrence 

of, 1 6 
Nephrite, characteristics and occurrence 

of, 18 
NeVe, 348 
Nigrine, characteristics and occurrence 

of, 64 
Niobite, characteristics and occurrence 

of, 46 

Nitrates, 55 
Nitratine, characteristics and occurrence 

of, 55 
Nitre, characteristics and occurrence of, 

55 

Xorite, characteristics of, 151, 156 
Nosean, characteristics and occurrence 

of, 15 

Nosean-melanite rock, 144 
Xovaculite, 267 



ABSIDIAN, pure, 185 

characteristics and occurrence of, 
197 

varieties, according to differences of 
texture, 197 

Ochre, yellow, 341 

red, 343 
Oilstone, 267 

OLgoclase, characteristics and occur- 
rence of, 1 1 

Oligoclase-dolerite, 138 

Olivine, characteristics and occurrence 
of, 38 

Omphacite rock, 318 



PHA 

Omphazite, characteristics of, 19 
Oolite, formation of, 94 

varieties of oolites, 284 
Oosite, occurrence of, 44 
Opal, characteristics of, 7, 349 

occurrences and mode of formation of, 
7, 349 

varieties of, 349 
Ophicalcite, 278 
Ophiolite, 314 
Ophite, 156 

Organic compounds, 76 

Ortliite, characteristics and occurrence 
of, 43 

Orthoclase, characteristics and occur- 
rence of, 9, 355 

varieties of colour and lustre of, 9 
Ottrelite, characteristics and occurrence 

of, 26 

Ottrelite-schist, 256 
Oxides of elements of the hydrogen 

group, 60 

anhydrous, 60 

hydrous, 66 
Oxydulated iron, 61 
Oxygen compounds, 5 



TJALAGONITE, occurrence of, 19 
-*- ' Paragenesis ' of minerals, 3 
Paragonite-schist, 244 
Parrot-coal, 332 
Paulite. See Hypersthene 
Pea.ore, 341 
Peastone, 282 

Peat, characteristics and occurrence of, 
324, 327 

varieties of, 328 

Pebbles, formation of, 102, 304 

Pegmatite, 206 

Pegmatolite, characters and occurrence 

of, 9 

Peperino, 308 
Pencil-slate, 264 
Pennine, 25 
Peridot, characteristics and occurrence 

of, 38 
Perlites, and Pearlstone-porphyry, 184 

characteristics and occurrence of, 
196 

varieties in texture of, 196 
Perofskite, characteristics and occur- 
rence of, 45 

Petrosilex, 220 

Phacolite, characteristics and occurrence 
of, 30 



422 



GENERAL INDEX. 



PHE 

Phenakite, or Phenacite, characteristics 
and occurrence of, 39 

Phengite. See Potash-mica 

Phillipsite, characteristics and occur- 
rence of, 32 

Phlogopite, 24 

Pholades, on the sea-coast, 102 

Phonolite group of rocks, 198 

Phonolite, Clinkstone, characteristics 
and occurrence of, 198 

varieties in texture of, 200 
Phosphates, 53 

anhydrous, 53 

hydrous, 54 

Phosphorite, characteristics and occur- 
rence of, 53, 353 

Finite, occurrence of, 44 

Pinsill, or Pencil-slate, 264 

Pistacite in hornblendic and pyroxenic 
rocks, 20 

characteristics and occurrence of, 42, 
355 

Pitchstone and Pitchstone-porphyry, cha- 
racteristics and occurrence of, 223 

varieties in texture of, 225 
Pleonaste, 60 

Plumbago, characteristics and occurrence 
of, 75, 336 

Plutonic rocks, 111, 113, 114, 128 

Polianite, characteristics and occurrence 
of, 64 

Porcelain clay, 13, 354 

Porphyrite, characteristics and occur- 
rence of, 1 68 

Porphyrites, 168 

Porphyry, 96 

Portland-stone, 280, 284 

Pot-holes, formation of, 101 

Potash-mica, characteristics and occur- 
rence of, 22 

damourite, margarodite, 23 
Potstone, characteristics and occurrence 

of, 251 

Prehnite, characteristics and occurrence 
of, 31 

Protogine, 206 

Psilomelane, characteristics and occur- 
rence of, 67 

Puddingstone, 302, 304 

Pumice-stone, and its varieties, 97, 185, 
197 

Puzzulana, 308 

Pycnite, occurrence of, 35, 355 

Pyrites, characteristics and occurrence 
of, 72, 357 

in hornblendic and pyroxenic rocks 
20 



ROC 

Pyrites continued 

magnetic, 71 
white, 73 

hydrous, 72, 357 

arsenical, 357 

Pyroohlore, characteristics and occur- 
rence of, 45 

Pyromeride, or Ball-porphyry, 218 

Pyromorphite, 70 

Pyrope, characteristics and occurrence 
of, 40 

Pyroschist, 338 

Pyrolusite, 65 

Pyroxene, characteristics and occurrence 
of, 18 

varieties of, 18 

appendix to, 19 

hydrous products of the decomposi- 
tion of, 19 

differences between hornblende and 
pyroxene, 20 

QUARTZ, characteristics of, 5, 350 
common quartz, how found, 5, 350 

amethyst, 6, 350 

chalcedony, 6 

agate, 6, 350 

jasper, 6, 350 

flint, 6, 350 

chert, hornstone, 7, 350 

modes of formation of quartz, 7, 350 
Quartz-porphyry, Elvanite, characteris- 
tics and occurrence of, 215 

varieties in texture of, 217 

in composition of, 218 

Quartz-schist, characteristics and com- 
position of, 246 

varieties in texture of, 247 

RAINDROPS, traces of, on rocks, 101 
Randanite, 350 
Reddle, 62 
Rennsellaerite, 316 
Resins, 76 

Rhodonite, occurrence of, 356 
Rhoetizite, characteristics and occurrence 

of, 36 
Rbyolite, characteristics and occurrence 

of, 193 
Ripidolite, characteristics and occurrence 

of, 24 
Rock-salt, characteristics and occurrence 

of, 67, 351 

formations, 117 

varieties of, 352 



GENERAL INDEX. 



423 



ROC 

Rock-soap, occurrence of, 355 
Rocks, acidic, analyses of, 85 

basic, analyses of, 86 

composite, 1 

igneous, 127 

metamorphic, 227 

plutonic, 144, 201 

sedimentary, 1 1 5 
analyses of, 86 

volcanic, 131,182 

simple, 1 

accessory or non-essential, 1 

analyses of, 78 

microscopic, 78 

magnetic, 78 

chemical, 79 

physical structure of, 87 

texture of, 87 

peculiar states of rocks, 95 

concretionary structure of, 98 

special forms of external structure 
of, 99 

jointed structure of, 1 03 

stratification of rocks, 105 

shape and bedding of rock masses, 
106 

geological formations and groups of 
rocks, 111 

volcanic, 111 

the older, 112 

upper plutonic, 1 1 3 

lower plutonic, 114 

argillaceous, 115 

marl formations, 116 

limestone formations, 116 

sandstone formations, 116 

conglomerate formations, 116 

coal formations, 117 

rock-salt formations, 117 

crystalline schist formations, 

118 

great geological periods of de- 
posit, 119 

transitions and transmutations of 
rocks, 120 

classification of rocks, 123 

rocks of special character or bedding, 
313 

observations on the processes of rock- 
formation in nature, 359 

Roofing-slate, 264 
Rottenstone, 279 

Rounded stones, formation of, 202 
Rubellan, 24 

Rutile, characteristics and occurrence of, 
66 



S 



SED 

AL- AMMONIAC, characteristics and 
occurrence of, 68 

Sahlite, characteristics and occurrence of, 
18, 19 

Salt, common, characteristics and oc- 
currence of, 67, 351 

rock, 67 

Saltpetre, characteristics and occurrence 
of, 55 

Chili saltpetre, 55 
Sand, varieties of, 299 

characteristics and occurrence of f 
301 

Sandstone, the term explained, 97 

formations, 116 

characteristics and occurrence of, 
295 

varieties in texture, 295 

in composition, 297 

geological varieties of, 298 

San id inc. characteristics and occurrence 
of, /d 

Saponite, characteristics and occurrence 
of, 25 

Saussurite Qade\ characteristics of, 
11 

Scaglia, 283 

Scapoiite, characteristics and occurrence 
of, 41 

Schalstein, characteristics and occur- 
rence of, 311 

varieties of, 311 
Schiller-rock, 314 

Schist, the term explained, 97 
Schists, metamorphic crystalline, 227 

composition of, 227 

properties of, 228 

schorlaceous schist, 323 

observations on the processes of for- 
mation of metamorphic crystalline 
schists, 378 

contrasts between the catogenic and 
anogenlc transmutations of, 391 

Schorl, characteristics and occurrence 
of, 37, 323 

varieties in texture, 323 

in composition, 324 

Scolecite, characteristics and occurrence 

of, 33 
Scoria, 97 
Sedimentary and fragmentary rocks, 

259 

characteristics of, 259 

table of geological periods of, 260 

observations on the processes of the 
formation of, 374 



424 



GENERAL INDEX. 



Selenite, characteristics and occurrence 
of, 49 

Sericite, 23 

Sericite-schist, 256 

Serpentine group of rocks, 314 

Serpentine, characteristics and occur- 
rence of, 26, 314 

varieties of, 315 

Shale, the term explained, 97 

argillaceous, characteristics and oc- 
currence of, 268 

varieties in texture of, 268 
in composition of, 269 

geological varieties of, 269 

miners' terms for shale, 29 note 

bituminous shale, 338 
Shingle, formation of, 102 

Siderite, characteristics and occurrence 
of, 57, 345 

varieties in texture and composition 
of, 345 

Silicates, 8 

felspar section, 8 

augite section, ] 6 

mica section, 22 

hydrous magnesian silicates (talc 
section), 24 

zeolite section, 28 

andalusite section, 34 

garnet section, 38 
Silicon, oxides of, 5 
Slag, volcanic, 67 
Slate, the term, 97 

polishing, tripoli, 349 
Slates, varieties of, 264-266, 273 
Smaragd, characteristics and occurrence 

of, 39 

Smaragdite rock, occurrence and com- 
position of, 19, 318 

Smithsonite. characteristics and occur- 
rence of, 33 

Soapstone, characteristics and occurrence 
of, 25 

Soda, carbonate of, characteristics and 
occurrence of, 59 

Soda-mesotype, characteristics and oc- 
currence of, 31 

Sodalite, characteristics and occurrence 
of, 14 

Spar, heavy, characteristics and occur- 
rence of, 47, 352 

manganese, 356 

Spargelstein, characteristics and occur- 
rence of, 53 
Sparry iron-ore, 57 



TIM 

Spathic iron, characteristics and occur- 
rence of, 57, 345 

varieties in texture and composition, 
345 

Sphserosiderite, 58, 346 

Sphalerite, 70 

Sphene, characteristics and occurrence 
of, 46 

Spinel, characteristics and occurrence 
of, 60 

Spodumene, characteristics and occur- 
rence of, 21 

Killinite, 22 
Stalactites, formation of, 99 
Stalagmites, formation of, 100 
Stassfurtite, occurrence of, 52, 353 
Staurotide (Staurolite), characteristics 

and occurrence of, 36 
Steatite, characteristics of, 27, 354 
Stilbite, characteristics and occurrence 

of, 33 

Stilpnosiderite, 67 
Strahlstein. See Actinolite 
Stratification ot rocks, 105 
Styolites, 99 
Sulphates, 47 

anhydrous. 47 

hydrous, 49 

Sulphur, characteristics and occurrence 

of, 74, 358 
Sulphurets, 69 
Syenite group of rocks, 176 
Syenite, characteristics and occurrence 

of, 177 

varieties in texture of, 178 



TALC section of minerals, 24 
-*- Talc, characteristics and occurrence 
of, 27, 354 

varieties of, 27 

Talc-schist, characteristics and occur- 
rence of, 251 

varieties of, 252 
Talc-spar, characteristics of, 57 
Tantalates, or Columbates, 45 
Tautalite, characteristics and occur- 
rence of, 45 

Teschinite, 148 

Tholeite, 138 

Thomsonite, characteristics and occur- 
rence of, 31 

Thumite, characteristics and occurrence 
of, 43 

Timazite (Trachytic Greenstone), cha- 
racteristics and occurrence of, 156 



GENERAL INDEX. 



425 



TIN 

Tin-ore, Tinstoue, characteristics and 
occurrence of, 65 

Tinkal, characteristics and occurrence 
of, 52 

Titanic iron-ore, 63 

Titaniferous iron, characteristics and 
occurrence of, 63 

Titanite, characteristics and occurrence 
of, 46 

Titanites, 45 

Tonalite, 207 

Topanhoacanga, composition of, 343 

Topaz, characteristics and occurrence 
of, 35 

Topaz rock, 306, 324 

Tourmaline, characteristics and occur- 
rence of, 37 

Trachyte group of rocks, 183 

varieties of, 184 

Trachyte, characteristics and occurrence 
of, 189 

varieties in texture, 189 

in composition, 190 

Trachyte-porphyry, characteristics and 

occurrence of, 194 

varieties in texture of, 195 
Travertine, 282 

Tremolite, characteristics and occurrence 

of, 17 

Tripestone, 291 
Triphane, characteristics and occurrence 

of, 21 

Tripoli, 349 
Trona, characteristics and occurrence of, 

59, 352 
Tuff, Tufa, the terms explained, 97 

characteristics and occurrence of, 306 

volcanic tufas, basaltic and trachytic, 
308 

tuff formations of plutonic rocks, 309 

siliceous, 349 
Turf, 327 

Turquois, characteristics and occurrence 
of, 54 



TTLTRAMARINE, characteristics and 

occurrence of, 17 
Uralite, characteristics and occurrence 

of, 18 
Urao, characteristics and occurrence 

of, 59 



ZWI 

yANADATES, 45 
' Vein, the term explained, 108 

Veins, mineral, and veins of ore, 392 

Vesuvian, characteristics and occurrence 
of, 41 

Vivianite, characteristics and occurrence 
of, 54 

Volcanic rocks, 111, 127, 131 

Volcanic tufas, basaltic and tracbytic, 
308 

Volbortbite, characteristics and occur- 
rence of, 47 



WACKE, the term explained, 96 
Wad, characteristics and occurrence 
of, 67 

Wavellite, characteristics and occurrence 
of, 54 

Wernerite, characteristics and occur- 
rence of, 42, 222 

Whetslate, Whetstone, 265 

Wiluit, characteristics and occurrence 
of, 41 

Wohlerite, characteristics and occurrence 
of, 46 

Woodstone, material of, 7 



^EOLITE section of minerals, cha- 
" racteristics, properties, and occur- 
rence of, 28 

monometric zeolites, 29 

hexagonal, 30 

t rime trie, 31 

monoclinic, 32 

Zinc, hydrous silicate of, 33 

carbonate of, 356 
Zinc-ore, red, 357 
Zincblende, 70 

Zinc-spar, characteristics and occur- 
rence of, 58 

Zircon, characteristics and occurrence 
of, 41 

Zircon-syenite, characteristics and oc- 
currence of, 181 

Zoisite, characteristics and occurrence of. 
41 

Zwitter rock, characteristics and occur- 
rence of, 322. 



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